Natural History of the Racer Coluber constrictor
by Henry S. Fitch · English · Gutenberg #42676 · 328,301 chars · public domain (US)
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Title: Natural History of the Racer Coluber constrictor
Author: Henry S. Fitch
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*** START OF THE PROJECT GUTENBERG EBOOK NATURAL HISTORY OF THE RACER COLUBER CONSTRICTOR ***
Transcriber's Notes
Emphasis denoted as _Italics_.
[M] and [F] represents the male and female symbols respectively.
Whole and fractional parts of numbers are represented as 41-3/4.
===================================================
University of Kansas Publications
Museum of Natural History
----------------
Volume 15, No. 8, pp. 351-468, pls. 19-22, 20 figs.
----------------- December 30, 1963 ----------------
Natural History of the Racer
Coluber constrictor
BY
HENRY S. FITCH
University of Kansas
Lawrence
1963
University of Kansas Publications, Museum of Natural History
Editors: E. Raymond Hall, Chairman, Henry S. Fitch,
Theodore H. Eaton, Jr.
Volume 15, No. 8, pp. 351-468, pls. 19-22, 20 figs.
Published December 30, 1963
University of Kansas
Lawrence, Kansas
PRINTED BY
JEAN M. NEIBARGER, STATE PRINTER
TOPEKA, KANSAS
1963
[Illustration]
29-7864
Natural History of the Racer Coluber constrictor
BY
HENRY S. FITCH
CONTENTS
PAGE
Introduction 355
Acknowledgments 357
Methods and Materials 358
Description 362
Color pattern 362
Bodily proportions 365
Lepidosis 367
Dentition 369
Hemipenis 369
Relationships 370
Range 371
Geographic Variation 373
Habitat 375
Temperature Relationships 377
Home Range and Movements 385
Food Habits 394
Methods of obtaining prey 394
Composition of food 395
Kinds of prey 403
Reproduction 408
Sexual behavior 408
Cycle of the male 414
Eggs 416
Hatching 423
Growth 425
Mortality Factors and Adaptations for Survival 432
Defense and escape 432
Natural enemies 438
Disease 442
Parasites 442
Populations 445
Composition 445
Numbers 450
Summary 456
Literature Cited 461
Introduction
Throughout much of the United States the racer is abundant and is one
of the snakes best known to man. Its active diurnal habits and its
preference for a habitat in meadows, pastures, and hayfields rather
than in remote wilderness areas, result in frequent encounters with
humans. The racer is a predator on many kinds of small animals, both
vertebrates and invertebrates; it takes as food chiefly animals that
are agricultural pests but also destroys some beneficial kinds. Yet,
in general, the attitudes of rural people toward the racer are little
influenced by these economic and ecologic considerations, but rather,
are dominated by an unreasonable fear, despite the racer's inoffensive
disposition, and inability to inflict any harm on humans.
Although an extensive literature exists regarding the racer, no
thorough study of the species' natural history has been made
heretofore. Obviously such study is needed. Few species of vertebrates
having comparable economic bearing have been similarly neglected. In
1948, undertaking a program of ecological research on the recently
created University of Kansas Natural History Reservation, I included
the racer among the many common species studied to gain insight into
the functioning of the local ecosystem. Live-trapping of snakes on the
area was begun in 1949, and these operations were greatly intensified
in the years 1957 through 1962, with efforts concentrated on the study
of the racer in the 1960, 1961 and 1962 seasons. Thus my study is
based upon 14 consecutive years' records on the Reservation, the
northeasternmost section in Douglas County, Kansas, six and one-half
miles north northeast of the University of Kansas campus at Lawrence.
After the acquisition in 1956 of the 160-acre Rockefeller Tract
adjacent to the Reservation on the north in Jefferson County, field
work was extended to this new area, which, because it was superior
habitat, in the final years of the study produced more records than
the Reservation. An important but relatively minor segment of the data
originated from Harvey County Park, 13 miles west of Newton, Kansas,
where lines of live-traps were maintained in 1959, 1960, 1961, 1962.
Smaller collections of data were obtained from the Lalouette Ranch in
the Flint Hills, three miles northeast of Florence, Marion County,
Kansas, and from Cedar Bluff Reservoir, 23 miles west and seven miles
south of Hays in Trego County, western Kansas, where live-trapping was
carried on in 1959 and 1960. Additional data were obtained on
numerous field trips to various collecting localities in northeastern
Kansas. My first-hand knowledge of the species is also based, in part,
on many years of field experience with the far western subspecies _C.
c. mormon_ in western Oregon and California, and on similar experience
in 1947 and 1948 with the southern subspecies, _C. c. anthicus_ in
central Louisiana.
This varied field experience with the species at localities well
scattered throughout its geographic range has added perspective to the
study even though most of the records were collected within a radius
of three quarters of a mile. No one locality can be regarded as
entirely typical of a species' habitat over its range as a whole.
According to my philosophy, the ecological niche of a species is
subject to geographical variation analogous to the variation to be
seen in the morphological characters of the animal itself. Different
community associates, including different competitors, prey, and
predators, and different physical factors enforce a somewhat different
way of life on a species in geographically remote parts of its range.
When analyzed these differences often turn out to have a genetic
basis. Thus, limits of tolerance to heat, cold, and drought often vary
geographically, and the population density, reproductive potential,
seasonal cycle, and other properties of populations may be altered
either by the direct effect of the environment, or through its effect
on the genetic constitution, produced by natural selection.
The local population of racers studied was near the center of the
species' geographic range, and is to some extent representative of the
species as a whole, though differing in its ecology from other
populations in proportion to their remoteness and the distinctness of
their habitats. It has not been demonstrated that ecological traits of
populations change in a discontinuous manner or correspond in their
limits with those of named subspecies. More likely geographical
variation is continuous and parallels morphological variation only in
a general way. Certainly the boundaries of subspecies' ranges should
not be accorded undue emphasis in an ecological study.
My investigation of the blue racer under natural conditions, combined
with a compilation and analysis of published literature, has resulted
in a fairly satisfactory understanding of some phases of the species'
ecology and natural history, such as the food habits, the growth rate,
the extent of home range and of seasonal movements. However,
relatively little was learned concerning some phases of the life
history. Unfortunately, the traps used did not catch young of the
smaller sizes. Facts concerning egg-laying, incubation, and hatching
therefore are known chiefly from snakes kept in confinement. Although
first-year young were captured by hand from time to time they were
obtained in relatively small numbers, and little was learned regarding
their population density, movements, or mortality factors. Of course,
such hiatuses are to be expected; even in man such enigmas as the
disparate sex ratio still challenge the investigator.
For the subspecies of racer involved in my field study the widely used
vernacular "blue racer" has been adopted in this report. In general I
advocate conformity with the vernacular names published by the
Committee on Herpetological Common Names (1956). However, in this
list, the name blue racer was assigned to _Coluber constrictor foxi_,
an invalid subspecies of the Prairie Peninsula that has been relegated
(Auffenberg, 1955:92; Smith, 1961:196) to the synonymy of _C. c.
flaviventris_. It therefore seems appropriate that the book name
"yellow-bellied racer" applied to _flaviventris_ by the Committee
should be abandoned for this subspecies, and that the name blue racer
be applied officially, as it is in actual practice by both laymen and
herpetologists, to all populations of this subspecies.
Acknowledgments
Financial assistance from the National Science Foundation in 1957
through 1962 is acknowledged. Although none of the three separate
grants involved was made specifically for the autecological study of
the racer, all three contributed to the support of the extensive
program of live-trapping for snakes, which yielded most of the records
upon which this report is based. Student assistants who were employed
on these projects include James W. Bee, William N. Berg, Donna M.
Hardy, Robert M. Hedrick, Dale Hoyt, Robert M. Packard, Robert G.
Webb, and Wayne Wiens, at the Reservation; Roy Henry, Dale Horst,
Dwight R. Platt, and Howard L. Schrag at Harvey County Park, and
Gilbert L. Adrian at Cedar Bluff Reservoir. Dr. Edwin P. Martin,
formerly of Fort Hays, Kansas State College, was helpful in planning
and carrying out the field work at Cedar Bluff Reservoir. Eric
Shulenberger assisted with field work and processing of data in 1962
under the National Science Foundation program for Undergraduate
Research Participation. Robert Miner assisted with the examination of
specimens in 1960. Mr. August Lalouette of Florence, Kansas, permitted
field work on his ranch and contributed information and materials to
expedite this work. Mr. and Mrs. Harold Brune of Route 3, Lawrence,
Kansas, kindly contributed several clutches of racer eggs found on
their farm in Jefferson County, and also made available significant
information accompanying them. Dr. William H. Stickel kindly made
available at my request records of predation on racers from the food
habits files of the U. S. Fish and Wildlife Service. Dr. William E.
Duellman of the University of Kansas Museum of Natural History and Dr.
Robert C. Stebbins of the University of California Museum of
Vertebrate Zoology kindly permitted examination and dissection of
specimens in the collections under their care. Dr. George W. Byers of
the University of Kansas Department of Entomology identified numerous
insects eaten by racers. My daughter, Alice V. Fitch, often assisted
me with the field work and the processing of data. My wife, Virginia
R. Fitch, read the manuscript critically, assisted me with the
examination of museum specimens, and with typing, and helped in
various other ways.
Methods and Materials
Table 1. Numbers and Distribution of Captures and Recaptures of Blue
Racers on the Reservation and Rockefeller Tract
=======================+=========================+=======================
Span of years within | Number of separate | Number of times
which each individual | years within which each | each individual
was captured | individual was captured | was captured
---------+-------------+-----------+-------------+----------+------------
| | | | Times |
Years | Individuals | Years | Individuals | captured | Individuals
---------+-------------+-----------+-------------+----------+------------
1 | 749 | 1 | 749 | 1 | 679
2 | 137 | 2 | 197 | 2 | 181
3 | 56 | 3 | 51 | 3 | 93
4 | 32 | 4 | 15 | 4 | 31
5 | 19 | 5 | 6 | 5 | 7
6 | 13 | 6 | 1 | 6 | 14
7 | 7 | 7 | 0 | 7 | 8
8 | 2 | 8 | 1 | 8 | 4
9 | 3 | | | 9 | 1
10 | 0 | | | 10 | 0
11 | 1 | | | 11 | 0
12 | 1 | | | 12 | 1
| | | | 13 | 0
| | | | 14 | 0
| | | | 15 | 0
| | | | 16 | 1
---------+-------------+-----------+-------------+----------+------------
This investigation was based primarily on the capture in live-traps,
marking, release, and recapture of blue racers in their natural
habitat. On the combined area of the Reservation and the Rockefeller
Experimental Tract, 1020 blue racers were recorded a total of 1688
times from August 30, 1948, to October 27, 1962. At Harvey County Park
361 blue racers were marked, and were captured a total of 467 times
from May 6, 1959, to September 14, 1962, and at Cedar Bluff Reservoir
42 were captured from May 11, 1959, to June 30, 1960.
The traps used were cylinders of galvanized wire, "hardware cloth"
(Fitch, 1951:77; 1960:77), having funnels opening into each end, or
having a funnel at one end and a plug at the other. The traps, open at
both ends, were used along hilltop rock ledges where an exposed
vertical rock face provided a barrier along which a snake might travel
and where it could be easily intercepted by the trap without any
accessory equipment (see Pl. 21, Fig. 1). Where such natural barriers
were lacking, as in level fields, barriers consisting of boards,
screens or sheet metal were installed to guide the racer toward the
trap and into a funnel entrance. Two such barriers at each end of a
trap forming a V to guide the snake into the funnel were used in 1956
and 1957, when trapping at places away from the hibernation ledges was
undertaken. Later it was found simpler and more effective to use a
single barrier with a trap at each end. The barrier extended up into
the funnel entrance, and usually the racer, following along the
barrier on either side, would pass into the funnel and through its
apex. However, it was possible for a racer to travel around the end of
the barrier without entering the trap, and perhaps some did so.
The need for making the barrier and trap a tight unit impassable to
the snake, was somewhat counterbalanced by the need for having the
whole installation loosely constructed so that it could be easily
altered, opened, adjusted, and cleaned. Since the traps were kept set
in large numbers, and the task of checking them was time-consuming,
speed of operation was more important than the perfect functioning of
any one trap. Approximately 200 traps were kept set when operations
were at their maximum. No record was kept of the number of "trap days"
involved in the study, but the total was well over 100,000 for the
Reservation and the Rockefeller Tract. When traps were set at both
ends of a barrier, the outer end of each trap was closed with a plug.
No bait was used in the traps. Occasionally small vertebrates and
insects of kinds used as food by the racers may have gotten caught
first and served to attract the snakes. Best catches of racers were
made in the breeding season, since males were attracted by females
already in the traps, and several males might be captured
simultaneously with one female. Occasionally as a person approached or
handled a trap, a racer darted out of it, displaying a perception,
acuity of vision, and skill in avoiding the inward projecting wire
prongs encircling the small funnel opening, that were exceptional
among the several species of snakes trapped. Doubtless many other
racers that were caught in traps escaped before they were discovered.
If the funnel entrance of the trap was of the same diameter as the
snake itself, or only a little larger, there was little likelihood of
the trapped racer escaping. However, funnel openings were usually
adjusted at a diameter of approximately 1-1/4 inches, allowing an
ample margin for even the largest racers, though inadequately small to
permit ingress of a few of the largest black rat snakes, bull snakes
and timber rattlers occurring locally.
Ordinarily the snakes trapped were processed in the field and released
immediately. The method of marking was essentially that of Blanchard
and Finster (1933:334). Two subcaudals, one on the right side and one
on the left, were clipped on each snake, and when these marks healed
they left permanent scars. In the racer, as in most other colubrines,
the subcaudals are divided into a double series, one on the left and
one on the right. Scales of the left and right sides are placed
alternately. At the base of the tail one or more undersized scales
usually are present on each side, and there might be some question as
to precisely where the count should begin. The rule followed was to
exclude from the count any small basal scales on either side that did
not extend medially to contact at least one scale of the opposite
side. The scale designated as "one left" (or "one right") was the
first to contact one of the opposite series, regardless of whether the
former was of normal size or (as was usually the case) smaller and
narrower than those following it. In marking, this "number one" scale
was never clipped but was left as a point of reference since a base
mark was needed from which to begin the count. The marks were read
from left to right, for example U 5_l_ 2_r_, the "U" referring to the
subcaudals or "urosteges," the "5_l_" indicating the fifth on the left
side, and "2_r_" indicating the second on the right. The subcaudals
clipped were the first 19 following the basal scale. When the 361
possible combinations all had been used, ending with U 20_l_ 20_r_, a
new series was begun duplicating the first except that on each snake
the first ventral (or "gastrostege") anterior to the anal plate was
clipped on the left side (G1L) to distinguish these snakes from the
series previously marked. Later, a third series, "G2R" was marked,
and eventually a fourth series, "G3L" was started.
There were many borderline instances in which the basal scale barely
contacted one of the opposite side. In such instances the formula was
written U 5_l__{ISB} 2_r_, the subscript ISB signifying "including
small basal." In other instances a basal subcaudal barely failed to
contact a scale of the opposite side and this condition was indicated
by the subscript NSB--"not including small basal." The condition might
be so nearly equivocal that on successive occasions the same formula
might be read U 5_l__{ISB} 2_r_ and U 4_l__{NSB} 2_r_. Occasional
misidentifications of individuals that resulted from such
discrepancies were in most instances readily detected when the field
records were transferred to individual file cards where the sex, size,
and location of the snake at its previous captures were shown.
In some instances racers recaptured after periods of years retained
conspicuous scars where scales had been clipped, but in other
instances the marks had become obscure, and in fact the only trace of
a mark might be a slight narrowing or notching of part of the scale
originally clipped. Snakes caught and marked early in life probably
retained more power of regeneration than those clipped after the
attainment of maturity, but otherwise the basis for difference in
extent of regeneration was not evident. In the same snake, three
scales, all clipped on the same day, might show much different degrees
of regeneration after the lapse of a year or more. In general,
obscuring of marks by regeneration was a source of inconvenience
rather than of error; only a negligible percentage of the recaptured
racers had marks so obscure that their identities might have been
seriously questioned, and it is doubtful that any marks were lost
completely by regeneration.
Racers found in traps were removed, measured (snout-to-vent length,
tail length), weighed in a cloth bag suspended from spring scales, and
marked. The mouth was forced open and the snake was examined for
flukes. Enamel paint of a bright color, red, green, yellow, blue or
orange was smeared on the snake to gain information regarding the time
of molt. The stomach was palpated for recently ingested food items,
and any detected were forced up into the gullet to be identified, then
were squeezed back into the stomach. The rear part of the body was
palpated to detect undigested material in the gut, and if any was
present, an attempt was made to squeeze out the fecal material, using
only light pressure, with care not to injure the racer. The inside of
the trap and the ground beneath it were inspected for fecal material
that might have been voided while the snake was confined. Any
scatological material obtained was wrapped in a paper towel, labelled
and brought back to the laboratory where it was stored. Eventually
each scat was soaked for a day or more in a detergent solution, rinsed
in running water in a fine gauze bag, dried, and placed with its label
in a cellophane envelope for subsequent microscopical study.
Various items concerning reproductive condition were also routinely
recorded. In females the ventral surface was palpated at the rear end
of the body to detect the genital bursa or vagina, which in sexually
mature individuals has a much thickened wall, and can be felt as a
distinct lump. Males were likewise tested for sexual maturity by
pipetting a small amount of fluid from the cloaca into a vial and
returning it to the laboratory where it was examined microscopically
for motile sperm. Also, sperm samples were often taken from males at
different times throughout the season of activity, and cloacal samples
from females occasionally were checked for sperm as evidence of recent
copulation.
In the summer of 1962 an outdoor enclosure of 100-foot circumference
was constructed, of galvanized sheet iron, with wall three feet high,
set on a concrete base extending to a depth of two feet. A
two-foot-deep concrete basin inside the enclosure served as a water
container. The enclosure was partly shaded by a large walnut tree and
the area enclosed had lush vegetation, including brome grass, various
shrubs, and young trees up to 15 feet high, thus including most
features of the racers' habitat, and it was situated in an area
frequented by the snakes. Throughout the summer several racers were
kept in the enclosure, and frequent observations on them yielded much
information concerning time of activity, temperature preferences, and
social and sexual behavior that could not have been obtained readily
either from racers confined in small cages or from those free under
natural conditions.
Description
_Color Pattern_
Hatchling racers differ much in appearance from adults; whereas the
latter are of dull uniform coloration dorsally, the hatchlings have a
checkered pattern of alternating blotches in several rows, including a
middorsal row, with blotches much larger than those of the other
rows. This basic pattern is perhaps the most common one in all snakes,
and is found in the young of various other genera (notably _Elaphe_)
which lose or alter their markings during development. In these genera
and in the racer, the juvenal checkered pattern may represent
recapitulation of an ancestral condition. The adaptive significance of
having a blotched, checkered pattern in the young, and uniform
coloration in the adult is not evident. I have rarely seen the
hatchlings under natural conditions except by finding them hiding
beneath flat rocks. Their concealing pattern must be fully as
effective as that of adults and the young themselves are more
secretive than the adults.
A hatchling of 240 millimeters snout-vent length was described as
follows on September 22, 1962: Ground color pale olive anteriorly,
gradually darkening posteriorly, marked with chocolate blotches;
middorsal blotches largest averaging about five scales long and seven
or eight scales wide anteriorly; posteriorly, blotches become less
distinct (tending to blend into progressively darkening ground color),
and width-to-length ratio increases; gradual obscuring of blotches
proceeds posteriorly, until on tail they can no longer be
distinguished, and color is uniformly olive; on each side, row of
lateral blotches alternates with that of middorsal blotches; lateral
blotches average somewhat less than two scales long, and approximately
two scales wide and are of irregular shape, sometimes subdivided;
farther down on sides, lower row of lateral blotches alternates with
upper lateral row; this lower lateral row, approximately same size as
upper lateral row, and situated at level of first scale row,
overlapping onto ventrals, where it pales to reddish brown; almost
every ventral scute has one pair or more of dark reddish brown spots,
tending toward semicircular shape, the arc of each projecting forward,
but posteriorly on body these spots become increasingly obscure, and
are indiscernible on posterior end of body and on tail; ventral
surface white on chin and throat, gradually assuming suffusion of pale
greenish gray posteriorly; eye dark with narrow yellowish margin
around pupil; top of head grayish olive, mottled with faint and
irregular dark markings; supralabials whitish, with chocolate
markings, mostly wedge-shaped, in their posterior parts; rostral and
internasals edged with dark posteriorly; posterior upper corner of
loreal and adjacent corner of prefrontal dark; temporals having dark
markings; chin almost immaculate, but with narrow black posterior
edges on some of the infralabials (see Plate 19, Figs. 1 and 2, and
Plate 20, Fig. 2).
The checkered pattern of the juvenile fades gradually as development
proceeds. Persistence of the juvenal markings varies greatly in
individuals and probably is subject to geographic variation also. By
the time sexual maturity is attained the dorsal pattern often is
indiscernible or represented only by faint traces. The ventral
speckling is more persistent.
A female of 602 millimeters snout-vent length in mid-July 1962, at a
probable age of 11 months, was described as follows: Overall dorsal
color olive gray, but with remnants of juvenal pattern discernible;
dark dorsal blotches have almost faded, but their edges, about one
scale wide, are still distinct; low on sides, color fades to pale
bluish gray, and to pale greenish blue on edges of ventrals; on
anterior one-third of body midventral surface is lemon yellow; farther
posteriorly it fades to ivory, almost white on tail; chin white,
except for reddish brown posterior edges of last infralabials, and
streak of same color on each antepenultimate infralabial; top of head
olive gray with irregular scattered dark marks; preoculars pale
centrally with olive brown edges; supralabials white with reddish
brown triangular marks; postnasals white anteriorly, gray posteriorly;
uppermost postocular brownish orange, paler centrally; two rows of
semicircular spots on belly, distinct anteriorly, but fading
posteriorly until indiscernible on posterior part of belly; numerous
small black spots scattered irregularly over dorsal and lateral
surfaces.
A male racer retained more of the juvenal pattern at an approximate
age of 15 months, when he was described on November 30, 1961: Dorsal
surface dark grayish brown, the large juvenal dorsal blotches (each
about eight scales wide) easily discernible, but faint; top of head
dark olive brown, mottled with black, paling in rostral region;
supralabials white on their anterior and lower portions, marked with
brown and blue-gray on their upper and posterior portions; chin white,
but with rusty markings on last four infralabials; ventrals
ivory-yellow with rusty spots of which the largest are approximately
three-fourths of the ventrals' breadth; first row of scales bluish
gray, or with greenish suffusion (in neck), most of scales having
indistinct dark spots; second row of scales similarly colored but more
suffused with dusky pigment, blending into the darker duller color of
the dorsal surface.
A female of 720 millimeters snout-vent length, presumably about 20
months old, but not gravid, on June 13, 1962, was described as
follows: Juvenal pattern no longer clearly discernible but scattered
traces of it remain; dorsal color predominantly grayish olive, with
occasional small black spots in streaks scattered irregularly over
dorsal and lateral surfaces; at anterior end of body lateral scales
have bluish green edges but this shading becomes less noticeable
posteriorly; head mostly olive dorsally with marking obscure;
parietals have a large faint blotch; supralabials retain faint dark,
brownish markings on their upper parts; dark spot on median edge of
each prefrontal; supraoculars slightly darker than adjacent scutes;
chin mostly white, with yellowish suffusion at edges of scales;
ventral surface predominantly yellow, but fading to grayish white
posteriorly; remnants of juvenal ventral spots faintly discernible as
tan or whitish areas on yellow ventrals.
Munro (1950b:124) mentioned a blue racer of 749 millimeters total
length (hence probably having a snout-vent length of 600 millimeters,
or a little less), which retained faint juvenal markings when caught
on June 23, 1948, even though it was sexually mature, since it laid
eggs on the night of July 4, 1948. During several weeks of captivity
this snake's markings faded perceptibly.
In fully adult blue racers, those more than three years old, the
juvenal markings have become completely obliterated. In those from the
area of my study, the dorsal coloration is subject to much individual
variation, typically olive brown, but ranging from pale bluish gray to
dark brown, dark blue, or slaty. In most, the dorsal color is uniform,
but in some there are streaks and isolated scales of black. The dark
dorsal color extends down the sides onto the lateral corners of the
ventrals and the subcaudals. The chin is white but the remainder of
the ventral surface is ivory colored.
_Bodily Proportions_
The slender and streamlined bodily proportions of the racer are
subject to change through allometric growth. The head, and especially
the eyes, are relatively large in the hatchling, and become relatively
smaller as growth proceeds. The relative tail length seemingly
increases in the growing young and then decreases slightly in adults.
Snout-vent length and tail length were recorded in almost all the
racers examined, but other measurements were recorded in relatively
few. In many racers, especially the larger adults, tails had been
damaged and lacked their terminal parts. Often only the tip was
missing, but, of course, such individuals were not usable in the study
of proportions of the tail. Table 2 summarizes information concerning
relative tail length in 935 racers of both sexes and various sizes,
from northeastern Kansas. Nearly all measurements are from the live
snakes; a few are from recently killed individuals.
In hatchlings, the proportions of the tail are not noticeably
different in males and females, but data indicate that the snakes'
tails are approximately seven per cent longer in males than in
females; as growth proceeds, the tails become relatively longer in
proportion to the body, in both sexes. The ratio reaches its maximum
in young adults, having increased from approximately 28 per cent of
the snout-vent length in males and 26 per cent in females, to 31 per
cent in males and a little more than 28 per cent in females. In the
largest racers, of both sexes, these percentages are slightly reduced.
Tail-length is subject to a fairly wide range of individual variation,
which tends to obscure the trends determined by sex and size.
Table 2. Relative Tail Length in Male and Female Racers of Different
Size Groups
=============+============================+============================
| Males | Females
Snout-Vent +--------+-------------------+--------+-------------------
Length in | Number | Mean ratio of | Number | Mean ratio of
Millimeters | of | tail-length to | of | tail-length to
| racers | snout-vent length | racers | snout-vent length
-------------+--------+-------------------+--------+-------------------
150-200 | 7 | 27.3 ± .833 | 2 | 26.3
201-250 | 24 | 27.8 ± .490 | 23 | 25.9 ± .479
251-300 | 9 | 28.8 ± .634 | 4 | 26.6
301-350 | 20 | 29.8 ± .246 | 11 | 25.0 ± 1.060
351-400 | 8 | 28.8 ± .530 | 12 | 27.5 ± .404
401-450 | 6 | 27.8 ± .775 | 5 | 26.3 ± .357
451-500 | 12 | 29.7 ± .434 | 6 | 26.8 ± .858
501-550 | 45 | 30.5 ± .283 | 15 | 27.6 ± .284
551-600 | 76 | 31.0 ± .218 | 35 | 27.1 ± .254
601-650 | 45 | 29.6 ± .313 | 64 | 27.8 ± .163
651-700 | 50 | 30.5 ± .241 | 36 | 27.1 ± .350
701-750 | 72 | 30.5 ± .177 | 45 | 27.6 ± .373
751-800 | 45 | 30.3 ± .373 | 38 | 27.8 ± .325
801-850 | 48 | 29.7 ± .274 | 50 | 27.5 ± .205
851-900 | 18 | 29.1 ± .519 | 35 | 28.6 ± .422
901-950 | 5 | 29.8 ± .672 | 31 | 26.7 ± .252
951-1000 | 1 | 29.5 | 19 | 26.9 ± .390
1001-1050 | .... | ..... | 15 | 25.9 ± .413
1051-1100 | .... | ..... | 6 | 26.4 ± .725
1101-1150 | .... | ..... | 1 | 28.5
1151-1200 | .... | ..... | 1 | 25.0
-------------+--------+-------------------+--------+-------------------
In 88 racers caught in the summer of 1962 the following measurements
were recorded: Head length, from tip of snout to angle of jaw; maximum
head width; greatest diameter of eye; circumference of neck;
circumference at mid-body; circumference at posterior end of body;
and circumference of tail-base. Because the measurements were small,
and were made in the field on active, struggling snakes, a high degree
of precision could not be attained, and the range of error was several
per cent, with occasional relatively large errors. Nevertheless,
ontogenetic trends are clearly indicated. Most of the racers measured
were adults of small to medium size--in the range 500 to 799
millimeters, snout-vent length. Twelve females and seven males ranged
from 800 to 1035 millimeters, and seven young (all females) were less
than 500 millimeters. In measurements other than circumference of
tail-base, significant differences could not be found between males
and females of the same size group; therefore the sexes were combined
to obtain larger series.
Table 3. Bodily Proportions (Expressed as Ratio of Snout-vent Length)
in Racers of Different Sizes
==========================+===============+===============+==============
| Large | Medium | Small
Size Group |(more than 800 | (500 to 800 |(less than 500
| millimeters) | millimeters) | millimeters)
--------------------------+---------------+---------------+--------------
Length of head | 3.61 ± .036 | 3.82 ± .025 | 5.39
Width of head | 1.93 ± .049 | 2.02 ± .023 | 2.53
Diameter of eye | .56 ± .008 | .63 ± .009 | 1.00
Circumference of neck | 4.71 ± .082 | 5.05 ± .052 | 6.64
Circumference at mid-body | 7.11 ± .238 | 7.66 ± .082 | 8.58
Circumference at posterior| | |
end of body | 5.06 ± .113 | 5.03 ± .061 | 5.90
Circumference of tail | 4.23 ± .113[1]| 4.22 ± .075[1]| 4.66[1]
at base | 4.47 ± .171[2]| 4.66 ± .043[2]|
--------------------------+---------------+---------------+--------------
[1] Females.
[2] Males.
Table 3 shows that as compared with adults, the small young racers
have stouter, stubbier bodies, relatively large heads, and,
especially, large eyes. Allometric growth seems to continue throughout
life and the changed proportions of the adults are accentuated in the
largest and oldest individuals.
_Lepidosis_
Scalation that of typical colubrid (see Pl. 19); rostral large,
extending back onto dorsal surface of snout, bluntly pointed behind;
paired internasals considerably wider than long, convex anteriorly,
almost straight-edged posteriorly, each extends laterally to naris;
paired prefontals approximately twice size of internasals, and wider
than long, extending laterally on each side to level of nostril;
frontal convex anteriorly, concave on each side, bluntly pointed
behind, nearly twice as wide anteriorly as posteriorly; parietals
large; angle formed between them by frontal slightly more than 90
degrees; nostril large, situated between almost equal sized anterior
nasal and posterior nasal plates; loreal slightly smaller than nasals,
its anterior edge inclined forward superiorly; two rows of temporals
on each side; in upper row, first one narrow and elongate, second much
shortened, third intermediate in shape; in lower row all three
approximately alike in size and shape; two postoculars, the lower
larger; seven supralabials, first small and low, longer along upper
edge than along lower, second slightly longer than high, third higher
than long, contacting eye; fourth largest, contacting posterior part
of eye, and lower postocular; fifth nearly as large, pointed above;
sixth also large, pentagonal; seventh low and rectangular; on chin
first pair of infralabials separate mental from anterior genials;
second infralabial minute; third approximately twice its size; fourth
much smaller, rhomboidal, fifth also large, pentagonal; sixth smaller,
rhomboidal, bluntly pointed behind; seventh smaller, narrow behind;
eighth small and elongate; second pair of genials longer and narrower
than those of first pairs, separated from each other by smaller
scales; genials in approximately five rows, but somewhat irregular in
arrangement, mostly smaller and narrower than body scales; latter all
smooth, arranged in 17 rows for about two-thirds of body length, then,
by loss of third row on each side, reduced to 15; scales of neck
region rounded and relatively small, one-third to one-fourth size of
larger body scales; lowest scale row on each side largest with its
scales much wider and less symmetrical than others; most of body
scales of approximately hexagonal shape; on forebody they average
approximately twice as long as wide, but farther posteriorly on body,
width-length ratio gradually increases and some of scales, notably
those of lowest row, approximately as wide as long; regularity of
scale rows broken on sides just above vent by presence of many small
additional scales; on tail scale rows drop out posteriorly in rapid
succession, until on posterior third only four are present; ventrals
strongly convex posteriorly, with free posterior edges, nearly half
length of scales; anal plate divided, with diagonal suture; subcaudals
in double series, those of right and left sides alternating; several
minute subcaudal-like scales on each side of vent.
_Dentition_
In the racer the maxillary, palatine, pterygoid, and dentary bones
bear teeth (Fig. 1). The teeth are all much alike in size and shape,
small, sharp, and recurved, typically at an angle of approximately 50
degrees. The number of teeth present is variable. Because the teeth
are small and loosely attached to the jaw bones, and often are broken
off in the capture and ingestion of prey, each bone usually lacks part
of its complement of teeth. Even the sockets vary somewhat in number
between individuals, and between the left and right sides in some
snakes. Most of the skulls that I examined were not thoroughly
cleaned, and the adherent dried tissues made it difficult to obtain
accurate counts of the sockets. In ten skulls from Kansas and
Nebraska, most frequently occurring numbers of sockets for each of the
dentigerous bones were: maxillary, 15; palatine, 11; pterygoid, 18;
dentary, 18.
[Illustration: Fig. 1. Lateral view of right side of skull of adult
female blue racer, × 4. University of Kansas Museum of Natural History
no. 18305, from Greenwood County, Kansas.]
_Hemipenis_
Penial characters have proven to be useful in the classification of
snakes, providing bases for separating subfamilies, genera, and
species. In the racer even the subspecies have trenchant penial
characters by which they may be separated in some instances. The
hemipenis is roughly cylindrical, but widest at the base (Fig. 2). The
sulcus spermaticus is unbranched. Approximately the basal one-third of
the hemipenis has a smooth surface, broken only by the sulcus
spermaticus and by three greatly enlarged spines, which form
hooks--one anterior, one posterior, and one dorsal. The dorsal hook is
the largest of the three. Distal to the smooth part is a zone of small
spines, each recurved and mounted on a fleshy tubercle. The zone of
spines is poorly developed on the anterior side and is interrupted on
the posterior side in the vicinity of the sulcus spermaticus but is
best developed on the posterior side a short distance above and below
the sulcus spermaticus. The spines are arranged in several oblique
rows. Those of the proximal row are best developed, and there is rapid
diminution in the size of those situated farther distally.
Approximately the distal two fifths of the hemipenis forms a third
zone, lacking distinct spines, but having numerous deep longitudinal
grooves, alternating with lamellae which have fimbriated edges, and
which fuse with each other and divide to form a reticulated pattern.
[Illustration: Fig. 2. Lateral view of injected and everted left
hemipenis (slightly enlarged) of a blue racer from the Rockefeller
Tract, Jefferson County, Kansas, showing heavy spines at base of
organ, small spines of central zone and lamellae of terminal part.
This hemipenis is not fully engorged.]
Relationships
The large genus _Coluber_ is much in need of revision. Its many
species, perhaps more than a score in all, occur in North America from
southern Canada south to Guatemala, in eastern and southwestern Asia,
in southern Europe, and in North Africa. All are active,
slender-bodied snakes having smooth scales in few rows, and having
large eyes with well developed vision. The North American species fall
into two natural groups, the typical racers, and the whip snakes,
often assigned to a separate genus, _Masticophis_ (Ortenburger, 1928).
The whip snakes are more specialized than the typical racers in having
the eyes more enlarged, and the body form more slender and attenuate,
with number of scale rows more reduced. The racers of the Old World
are more diverse. Inger and Clark (1943) suggested a partitioning of
the genus _Coluber_ on the basis of the pattern by which scale rows
are reduced, from the maximum number on the forebody to the minimum
number at the posterior end of the body, supplemented by certain
characters of the hemipenis and of the cephalic scutellation. Besides
_Coluber_ and _Masticophis_ these authors recognized within the group
the genus _Platyceps_ with several species in southern Europe and
southwestern Asia; _Zamenis_ with several species in the same region
and in North Africa, and _Haemorrhois_, a monotypic genus of Spain,
North Africa and several Mediterranean islands. Although apparently
valid in principle, this arrangement has not been generally followed.
Exclusive of those species groups whose assignment to the genus
_Coluber_ are somewhat questionable, the remaining species in the
genus are: _C. constrictor_ occurring throughout most of the United
States and south along a narrow Atlantic coastal strip of Mexico to
Guatemala; _C. oaxacae_ of southern Mexico; and _C. spinalis_ of
northern China. _C. oaxacae_ is poorly known as only a few specimens
have been collected, but seemingly it is a near relative and
derivative of _C. constrictor_, especially of that species'
southernmost population. _C. spinalis_ is much more distinct, as might
be expected from its geographical remoteness. It is a slender, active
snake, of olive coloration dorsally with 17 scale rows and a bright
yellow, black-edged dorsal stripe and yellow ventral surface. It is
relatively small (up to 755 millimeters snout-vent length) and is
partial to riparian habitats but is also found in forests and in dry
and barren regions (Pope, 1935:224-226). It is known to feed upon
lizards.
Range
The common racer has been recorded in each of the 48 states of the
mainland of the United States, also in New Brunswick, Nova Scotia,
southern British Columbia, and southward through Mexico where it is
limited to a narrow strip of east coast lowlands but extends as far as
Guatemala. _C. c. constrictor_ occupies the northeastern states and
extends south into the Appalachian and Piedmont. _C. c. priapus_ with
its associated races _paludicola_, _helvigularis_, and _anthicus_ has
an Austroriparian distribution, occupying the Atlantic Coastal plain
and the Gulf Region, and extending north in the Mississippi Valley to
southern Illinois and Indiana. _C. c. paludicola_ is localized with
two disjunct populations--in the Everglades and on Cape Canaveral,
Florida. _C. c. helvigularis_ is even more restricted in range and is
known only from the Appalachicola region of the Florida Panhandle and
the adjacent corners of Alabama and Georgia. _C. c. anthicus_ occupies
much of central and western Louisiana and adjacent Texas. _C. c.
flaviventris_ occurs throughout the Great Plains, east in the "Prairie
Peninsula" through Michigan and northern Ohio and west to the Rocky
Mountains. _C. c. stejnegerianus_ occurs from Matagorda Bay in Texas
southward through eastern Mexico, with a seemingly isolated population
in the Sierra del Carmen region of northern Coahulia. _C. c. mormon_
occurs in the Pacific Coast states and Great Basin.
Actually, the range limits and the continuity of distribution within
the area outlined are still poorly known. The species has not been
recorded from the northern parts of Maine, Vermont, New Hampshire,
Michigan, Wisconsin, or Minnesota, nor from northeastern New York. It
is generally absent from southwestern desert areas. Records are
particularly scarce and scattered in the Rocky Mountain states,
suggesting that the distribution in this area may be discontinuous. In
a large area comprising all of New Mexico and Arizona, the western
half of Colorado, and the southern halves of Utah and Nevada, records
are so scarce as to indicate that the species is there represented by
only a few well isolated relict colonies. The type locality of
_mormon_ is "Valley of the Great Salt Lake," and there are numerous
records from the northern part of Utah east of Great Salt Lake
(Woodbury, 1931:75), but a record from Moab is the only one known to
me from the southern half of the state. The only records from western
Colorado are from three miles east of Fruita and two miles west of
Grand Junction, Mesa County (Maslin, 1959:56). Apparently the only
valid record from Arizona is that of Shannon (1950:59) from Eagar,
Apache County, in the east-central part. Shannon also recorded the
racer from Boulder Dam in extreme southern Nevada. Brattstrom
(1955:152) has recorded the species from the lower Pleistocene of
southeastern Arizona (Curtis Ranch), bearing out the idea that the
racer has partly withdrawn from a range formerly occupied in the
Southwest at a time when cooler and moister climate prevailed. Other
fossil occurrences are of late Pleistocene age--Vero Beach and
Seminole, Florida (Brattstrom, 1953a:245) and, doubtfully, Rancho
LaBrea, California (Brattstrom, 1953b:376). The range of _mormon_ has
been mapped (Wright and Wright, 1949:134) as extending east to
south-central Montana on the basis of one specimen allocated on the
basis of two characters. Otherwise the range of _mormon_ seems to be
entirely west of the Continental Divide, well separated from that of
_flaviventris_ by desert and mountain barriers. The conspecificity of
_mormon_ with the other subspecies needs to be more thoroughly
investigated, and geographic variation within _mormon_ also merits
study.
Geographic Variation
The common racer and the several species of whip snakes
(_Masticophis_) were revised by Ortenburger (1928). More recently with
much larger series of specimens, Auffenberg (1955) again revised the
classification of _C. constrictor_, but his study was concentrated in
Florida and neighboring southeastern states with relatively little
attention devoted to populations of the western and central United
States. As the species occurs throughout most of the United States and
south through the coastal lowlands of eastern Mexico to Guatemala, it
is found over a wide range of environmental conditions. Various
characters are subject to geographic variation, and some of them
follow clines that are maintained over extensive areas. Such
characters as the number of hemipenial spines, and the enlargement of
one or more basal spines into hooks, the shape of the premaxillary
bone, the number of maxillary teeth, the numbers of ventrals and
caudals, color of eye, number of dorsal saddle-marks and of ventral
spots in juveniles, and ratios of body proportions including tail
length to total length have been used to characterize the subspecies.
Also important is the shade of coloration of adults. The subspecies
_constrictor_, _priapus_ and _helvigularis_ that are characteristic of
forested habitats in the eastern United States are black dorsally and
have their ventral surfaces suffused to a large extent with dark or
dusky coloring. Farther westward the ground color becomes
progressively paler, greenish, grayish or light brown, and the ventral
surface is yellow (white on the throat and neck). The same tendency
appears in _C. c. paludicola_ of the Everglades. The populations of
arid climates in southern Texas and in the far western states are
relatively pale colored. The species thus conforms to Gloger's Rule in
changing from a pallid coloration in arid climates to a dark pattern
with eumelanins predominating in a humid climate.
Perhaps the most important character that is subject to geographic
variation in the racer, and certainly one of the most neglected, is
body size. With information now available it is not possible to
compare the sizes of different populations except in a general way.
The best sources of information concerning size in several subspecies
other than _flaviventris_, are the publications of Auffenberg (1949
and 1955). Comparison of these data with my own is not entirely
satisfactory because Auffenberg did not indicate clearly differences
in size between the sexes, nor indicate the boundary line between
young and adults. Also, his measurements are of overall length. For
the purpose of comparison I have subtracted 22.5 per cent, an
approximation of ratio of average tail length, from Auffenberg's
figures. He stated (1955:98) that the series of specimens on which
measurements were based were those "with a uniform coloration," that
is to say they had lost the juvenal pattern and were probably sexually
mature. Whether the same statement applied to the large series of
_stejnegerianus_ in the same author's earlier paper (1949:55) is
doubtful.
_C. c. constrictor_: 34 New York specimens averaged 806
millimeters (Auffenberg, 1955:96).
_C. c. flaviventris_: 100 Kansas specimens averaged 791
millimeters (males, 746; females, 836).
_C. c. priapus_: 171 Florida specimens averaged 713
millimeters (Auffenberg, 1955:96).
_C. c. stejnegerianus_: 291 Texas specimens averaged 664
millimeters (Auffenberg, 1949:54).
_C. c. mormon_: 94 West Coast specimens (Museum of Vertebrate
Zoology) averaged 563 millimeters (males 515, females 600).
_C. c. anthicus_: 35 northern Louisiana specimens estimated
to average 582 millimeters (Clark, 1949:249--the author did
not present individual measurements, but indicated the
numbers in several size groups in his sample).
The 100 _flaviventris_ in the above list were recorded in June, July
and August, a season when the young of the preceding year are still
small, and these young were not included. In a fall sample 63 males
averaged 729 millimeters and 65 females averaged 886 millimeters, but
with the nearly grown young (44 males and 40 females) included, the
averages were changed to 651 and 768 respectively. Maximum length
perhaps express differences between the subspecies as well as, or even
better than, the averages listed above. The following figures indicate
some of the maximum overall length measurements in inches that have
been published by various authors. These measurements pertain to
females unless otherwise indicated.
_C. c. constrictor_: 74-3/4, 74-1/4, 73, 65-1/2 (Auffenberg,
1955:96).
_C. c. flaviventris_: 71 (Pope, 1944:172), 72 (Conant,
1958:147).
_C. c. priapus_: 52-1/2 ([M]) (Auffenberg, 1955:98).
_C. c. stejnegerianus_: 37 (Auffenberg, 1949:54), 40 (Conant,
1958:148).
_C. c. mormon_: 51-1/2 (Museum of Vertebrate Zoology).
_C. c. anthicus_: 70 (Conant, 1958:149).
In my own study, the largest racers recorded from the Reservation and
Rockefeller Tract had the following overall lengths: 59, 57-1/4,
55-1/2, 58 [M] (projected from stub tail).
These sets of figures show that compared with the blue racer in
Kansas, with which my own study was concerned, the black racer of the
northeastern states reaches a larger size, while the racers of the
Southeast and especially those of the far West and of southern Texas,
are dwarfed. These size differences are almost certainly correlated
with behavioral and ecological differences among the snakes involved.
Adaptations to exploit certain types of prey and to utilize most
efficiently certain habitats and types of cover, have led to divergent
trends in different parts of the range.
Habitat
The racer dwells primarily in open situations, but as might be
expected from its extensive geographic range, bringing it under the
influence of diverse climates and habitats, its populations have
diverged somewhat in adaptation to different environmental conditions.
The eastern blacksnakes (subspecies _constrictor_ and _priapus_) seem
to prefer woodland and forest edge. In central Louisiana, _anthicus_
occurs chiefly in an open type of woodland. The subspecies
_stejnegerianus_ is found chiefly in brushland and thorn forest. The
western _mormon_ is found in varied habitats, including moist
streamside meadows, and chaparral. Published statements of
herpetologists, based upon studies in limited areas, are briefly
quoted below to show the trend of geographic change.
_C. c. constrictor_: This snake "occurs chiefly in fields" (Atkinson,
1901:148; Pennsylvania); "in more or less wooded regions and along
hillsides and among bushes" (Surface, 1906:167, in Pennsylvania);
"abundant, especially in wooded regions" (Hibbard, 1936:28, in
Kentucky); "dry and more or less open places" (Conant, 1938:52, in
Ohio); "old fields and areas about buildings" (King, 1939:572, in
Tennessee).
_C. c. priapus_: In "drier parts of the [Okefinokee] swamp ... seems
to prefer blueberries and saw palmettos" (Wright and Bishop, 1915:159
in Georgia); "common in grassy fields and in upland woods" (Allen,
1932:13, in Mississippi); "abundant along fence rows ... in dry
pine-oak forest and in bottomland forest" (Trowbridge, 1937:296, in
Oklahoma); "probably most abundant in open upland hammock or in old
fields; limestone flatwoods" (Carr, 1950:80, in Florida); Oak and
oak-hickory forest and small hill prairies in southern Illinois
(Rossman, 1960:219).
_C. c. paludicola_: In "all parts of the freshwater Everglades, in
cabbage palm hammocks, in salt marshes, and in mangrove swamps. On Key
Largo ... in mesophytic hammock" (Duellman and Schwartz, 1958:296, in
southern Florida).
_C. c. anthicus_: In "wooded areas in the vicinity of briar patches or
other brushy undergrowth" (Clark, 1949:249, in northern Louisiana);
"especially grassy uplands" (Fitch, 1949:88, in central Louisiana).
_C. c. stejnegerianus_: Of 291, 94 were in scattered brush, 92 in
sparse brush, 41 in lightly wooded areas, 26 in grassy areas, 24 in
heavy brush, eight in semi-arid places and six in heavily wooded
situations (Auffenberg, 1949:55, in southern Texas).
_C. c. mormon_: In "thin brush skirting open prairie land" (Lord,
1866:304, British Columbia); cottonwood-willow and water margin
habitats in prairie (Dice, 1916:310-312, in eastern Washington);
"grass; amid water cress; bank of small ditch near meadow; barley
field; sandy ground covered with rocks and driftwood; among sedges; in
sagebrush; swimming in irrigation ditch" (Grinnell, Dixon and
Linsdale, 1930:149, in northeastern California); low foothills, around
the fields, and in the timber and brush along the canyon bottoms
(Woodbury, 1931:75, in Utah); "open woods of Garry oak and poison oak,
on grassy slopes, in chaparral, and in grain or hay fields" (Fitch,
1936:644, in southwestern Oregon); "low hot canyons where it was found
to occupy areas having rather dry, rocky hills" (Ferguson, 1952:68, in
northeastern Oregon).
_C. c. flaviventris_: Pastures, meadows, and fields (Hurter, 1911:170,
in Missouri); "usually frequents dry open fields, although it is often
found in bushes or cut-over land which has grown up into thickets"
(Ortenburger, 1928:181); "pasture lands and on hill sides" (Peters,
1942:183, in Illinois); "along the levees in the salt marshes" (Liner,
1954:82, in southern Louisiana); "common in both prairie and woodland
habitat" (Smith, 1947:34, in east-central Illinois); Flood plain, sand
around sage-sumac brush, rocky slopes (Fouquette and Lindsay,
1955:411, in northwestern Texas).
Several observers have described the habitat in Kansas as follows:
"grassy valleys and thinly wooded hillsides" (Burt, 1927:5); "moist
and dry habitats, in wooded areas, and in prairies" (Smith, 1956:237);
Oak-walnut hillside forest, cultivated field, buckbrush-sumac, prairie
(Clarke, 1958:22).
Every part of the 590-acre Reservation is used to some extent by blue
racers living on this area. Home ranges of most individuals are so
large as to include a variety of habitats, both woodland and
grassland. The habitat preferences vary according to season. In autumn
some racers migrating to rock ledges to hibernate are found in mesic
forest, but at that time of year leaves have begun to fall and the
forest floor is less dark and humid than in summer. In spring also
racers not yet back on their summer ranges are often seen either along
the hilltop ledges, or moving downhill through woods toward bottomland
meadows. However, in summer, the finding of a racer in mesic woodland
is a rare event. Occasionally the snakes make trips across such blocks
of woodland hundreds of feet wide, but they do not linger in the
woodland. In decreasing order of preference the habitats used by
racers on my study area may be classified as follows:
1. Tall-grass prairie, (Plate 22) either original or regenerated,
dominated by native perennial grasses in stands three feet to seven
feet high, including big blue-stem (_Andropogon gerardi_), little
blue-stem (_A. scoparius_) Indian grass (_Sorghastrum nutans_), and
switchgrass (_Panicum virgatum_).
2. Pastureland, with introduced brome grass (_Bromus inermis_) and
associated weedy vegetation.
3. Brush, in ravines, at woodland edge, and in riparian thickets.
4. Weedy fields, dominated by such pioneer plants as ragweeds,
sunflowers, horseweed, milkweed, wild lettuce, aster and goldenrod.
5. Open type of woodland dominated by such trees as honey locust and
osage orange.
These habitat types are interspersed on the study area, and each racer
has a wide choice of habitats without travelling beyond the limits of
its own chosen area.
Grassland that has been closely grazed, mowed or burned does not
provide entirely adequate food or shelter, and under such conditions
clumps of brush or other dense vegetation may be of critical
importance. Throughout the racer's extensive range, fields of grain
and hay at times provide suitable habitat, and may support large
populations, but in spring, before the young cultivated plants have
made much growth, or later in the season, after they have been cut,
the racer may need to depend on adjacent areas of pasture, thicket, or
woodland edge and the availability of such refugia to a large extent
determines the numbers of racers on cultivated areas.
Temperature Relationships
In the locality of my study racers spend approximately half the year
in winter dormancy. Earliest spring records and latest fall records
for 13 years are shown in Table 4. The spring records in nearly all
instances pertain to snakes found in the open or beneath flat rocks
warmed by sunshine, usually at or near the rock ledges where
hibernation occurs. Juveniles are especially well represented in these
earliest spring records, and it seems that they tend to emerge a
little earlier, on the average, than the adults, either because they
have hibernated in more superficial and less well insulated situations
or because their lesser body mass permits more rapid warming to
activity than can occur in the adults. The latest fall records all
pertain to racers trapped along the rock outcrops, and none was a
young of the year.
Table 4. Earliest and Latest Recorded Annual Dates When Blue Racers
Were Active on the Reservation or Rockefeller Tract
==========+==========+=============++==========+==========+============
| Earliest | Latest || | Earliest | Latest
Year | spring | fall || Year | spring | fall
| record | record || | record | record
----------+----------+-------------++----------+----------+------------
1950 | April 16 | November 4 || 1957 | April 30 | November 2
1951 | April 19 | November 13 || 1958 | April 25 | November 20
1952 | April 23 | November 12 || 1959 | April 6 | November 10
1953 | April 8 | November 12 || 1960 | April 22 | November 6
1954 | April 20 | November 12 || 1961 | April 19 | November 1
1955 | April 15 | November 2 || 1962 | April 23 | October 27
1956 | May 11 | November 14 || | |
----------+----------+-------------++----------+----------+------------
Most of the population undoubtedly emerged somewhat later than the
average date of April 16 indicated by the records in Table 4, and
retired somewhat earlier than the average date of November 8. However,
a small percentage of the population probably emerged even earlier
each year than my records indicate, and retired into hibernation later
than my records indicate. In a typical year, temperatures in April and
early May are only occasionally above the level at which racers are
able to become active, but are below this threshold most of the time.
The same statement applies to an autumn period of late October and
November. Most racers are dormant in their hibernacula during these
transitional periods of spring and autumn, but some--those that have
emerged early in spring, or those that have not yet retired (in
fall)--retreat to temporary shelters and revert to a semi-torpid state
when temperatures fall below the critical level.
Fig. 3 shows the relative extent of activity along the hilltop
outcrops, as reflected by numbers of racers caught at different times
during the autumn. Data from 14 years are combined, and the large
composite sample indicates that in an average year there is relatively
little activity along the hilltop outcrops in early September, but
that activity rapidly increases to a peak in mid-October and then
tapers off rapidly, usually ending in mid-November, but occasionally
ending as early as late October or as late as late November.
The racers recorded in traps had, in many instances, been confined in
them for from one to three days before they were found. For any one
year records are not sufficiently numerous to show the trend as well
as Fig. 3, but Fig. 4 shows year-to-year differences; 1958 was a
fairly typical year, and also was the year in which the largest sample
was obtained; in 1949 the largest catches were made earlier than
usual, and the racers retired early into hibernation; in 1954 warm
weather persisted until unusually late in autumn, and racers remained
active beyond the time when they ordinarily would have been
hibernating; in 1955 and 1961 the most concentrated activity along the
outcrops, as reflected by day to day catches, came later than usual,
but unseasonably cold weather ended all activity abruptly, earlier
than usual.
[Illustration: Fig. 3. Records of blue racers trapped along hilltop
limestone outcrops in autumn, a composite sample of 14 years (1949
through 1962) from the Reservation and Rockefeller Tract, showing the
catch grouped in ten-day intervals, beginning with September 1 to 10
and ending with November 20 to 29. Averages of the maxima, means, and
minima of daily temperatures for each period are shown.]
The racer's annual cycle of activity is, of course, controlled
primarily by the weather, and is much delayed or accelerated in some
years. But certain stabilizing factors cause the racer's annual cycle
to be less variable than that of the weather. For example, in spring
when persistently cool weather delays emergence from hibernation
beyond the normal time, the increasing azimuth of the sun, and more
intense sunshine cause the soil to warm, despite low air temperature,
until emergence is finally triggered. Having once emerged, the racer
is able to control its bodily temperature to a large extent by basking
in sunshine to gain warmth, or by seeking shade or underground shelter
to escape overheating. By such behavioral thermoregulation extremes of
weather are neutralized, or at least buffered to some degree.
[Illustration: Fig. 4. Yearly variation in catch of blue racers along
hilltop outcrop in autumn on the Reservation and Rockefeller Tract,
grouped in same ten-day intervals indicated for Fig. 3.]
In the course of my study no racers were found in their actual
hibernacula. Insofar as known, these were always in deep crevices in
strata of limestone near hilltops, and were inaccessible except by
removal of the solid rock. The crevices where racers hibernate are
known to be several feet deep in some instances, extending well below
the frost line. Periodic temperature readings in two such crevices at
depths of 12 inches and 30 inches, taken in the winter of 1954 (Fitch,
1956:471) showed that temperatures during dormancy are usually well
within the range 0°C to 10°. Whether the racers congregate in
hibernating masses in regular "dens" on the Reservation has not been
definitely determined, but if so, most of the hibernating groups must
be small, because those trapped along the ledges are well scattered,
and, in fact, give the impression of being rather uniformly
distributed along them. However, ledges of northward exposure are not
used as hibernation sites, so far as known, and those of full
southward exposure are perhaps preferred, especially where the hilltop
has a southward projecting spur, and the exposed rock face is
extensive, with many cracks and fissures. I have been unable to detect
differences in types of hibernation sites preferred between the racer
and the copperhead, which is somewhat more numerous on the same area.
Several authors have contributed to knowledge of hibernation in the
racer. Boyer and Heinze in Missouri (1934:195) noted that blue racers
often were associated with copperheads in the vicinity of places
chosen for hibernation. Burt (1935:329) in Kansas found blue racers
emerging from dens among rocks on a prairie hillside, associating with
other snakes, _Diadophis punctatus_, _Elaphe guttata_, and _Pituophis
melanoleucus_. In the Chicago region, Pope (1944:173) reported scores
of blue racers aggregating in October on and around a sand dune with
oak woodland. In Ohio, Conant (1938:55) found three blue racers
hibernating together about three feet underground in a small hole. One
found at another locality had apparently hibernated in company with a
massasauga (_Sistrurus catenatus_). In Maryland Cohen (1939:137) saw
racers (_C. c. constrictor_) in the act of emerging from an old vole
burrow that was a communal hibernaculum, on April 6, 8, and 10. Air
temperatures at the time of emergence were 12.5° and 18.5° Centigrade.
In Illinois, Schroder (1950:1-2) found seven blue racers hibernating
in masses, intertwined with each other and with bull snakes at depths
of 36 inches and 42 inches in an abandoned mammal burrow in a sand
dune area in early February.
[Illustration: Fig. 5. Bodily temperatures of blue racers kept in a
large outdoor enclosure and checked from time to time when they were
active and the sun was shining, in June and July, 1962.]
In the course of routine field work I often carried a Schultheis
quick-reading thermometer, and from time to time I had opportunities
to take the body temperatures of blue racers newly captured by hand.
The trend of these records indicated the temperature range within
which the snakes normally limit their activity, and the preferred
temperature. In an earlier publication (Fitch, 1956:459-460) based on
a few more than half the number of records of temperature now
available, I discussed responses of the blue racer to temperature. The
newer data bear out the trends previously revealed; of 60 records, 39
are within the six-degree range from 29° to 35°, and records are most
concentrated in the one-degree range, 34° to 35°. Racers were found
active at air temperatures between 15.5° and 32.4°, with the greatest
concentration between 26° and 27°. Compared with most other kinds of
North American snakes, the racer is remarkably tolerant of heat, and
often is several degrees warmer than the level that those of other
genera will normally tolerate. Racers have been seen crawling in the
sunshine, or basking on days that were uncomfortably hot for humans.
For example, on August 28, a large female racer released from a trap
was followed and her behavior observed; after crawling some 50 feet
through the grass she climbed from a ditch bank onto sunflower stalks
and elm saplings, and came to rest among the stalks, in a spot
strategically situated for catching grasshoppers. More than half her
body was exposed to sunshine and air temperature was slightly above
34° Centigrade, yet the snake showed no sign of discomfort, and for
the several minutes that she was kept under observation, did not
attempt to withdraw into the shade.
[Illustration: Fig. 6. Bodily temperatures of blue racers captured by
hand in their natural surroundings. The preferred level is
approximately the same as indicated by Fig. 5 (between 29° and 36°
Centigrade), but some of the racers caught were not fully active and
had lower temperatures. Some bias results from the fact that those
having the lowest temperatures were the least active and hence were
most easily caught.]
[Illustration: Fig. 7. Air temperatures recorded at captures of the
racers whose records were used in Fig. 6. An active racer typically
maintains, by basking, a bodily temperature several degrees warmer
than the air.]
[Illustration: Fig. 8. Bodily temperatures of blue racers found in
live-traps at Harvey County Park. Opportunity to regulate temperature
by behavior was limited in these snakes in traps, which tended to
match ambient temperatures.]
At the Harvey County study area, bodily temperatures were recorded in
many of the racers that were caught in traps. These records are much
less significant than the records obtained from racers caught by hand
and promptly checked for bodily temperatures. The temperatures of the
trapped snakes may, to a large extent, reflect the temperatures of air
and soil at the time. However, despite their confinement, the trapped
racers probably were able to exercise some control over their
temperatures by shifting from shade to sunshine, or from the top of
the trap to its bottom, where they would be in contact with the
substrate. In most of the racers removed from traps, as in those
caught by hand, bodily temperatures were somewhat above air
temperatures, but the difference was less in the former group of
snakes. Figure 8 shows the bodily temperatures of these snakes removed
from traps. Occasionally racers died in the traps from overheating. On
July 2, 1960, each of two racers in traps had temperatures of 39.4°.
One of these was especially vicious and frantic in its attempts to
escape, but otherwise seemed unharmed. The second racer was dead,
seemingly having succumbed just before it was found. Probably
prolonged exposure to temperature in excess of 39° would always result
in death of the snake. Racers and other snakes that had become
overheated in the traps and were nearing exhaustion had a
characteristic limp feel when they were handled. In June, 1960, heat
tolerance of a halfgrown racer was compared with that of several other
snakes including a copperhead, garter snakes, and ringneck snakes.
Each snake in turn was enclosed in a plastic tube plugged with cotton
at one end, the snake having a quick-reading thermometer taped in
place for a rectal reading. The tube was then placed in sunshine. Over
periods of minutes the enclosed snake passed through a characteristic
cycle. Soon it would begin to register discomfort as its temperature
rose rapidly. Its struggles would become increasingly violent, then
would cease abruptly. The snake would suddenly collapse, its body
mostly limp, but knotted in slow contortions, its mouth gaping widely.
Within a few seconds all movements would cease, but in each instance
the seemingly dead snake was soon revived by holding it in cold
running water. The copperhead, garter snakes, and ring-necked snakes
all collapsed at temperatures near 41°. At this same temperature the
racer showed signs of acute discomfort, but did not collapse even
after many minutes of exposure. Probably more protracted exposure at
this level would have been fatal to the racer as well as to the other
kinds tested.
Home Range and Movements
Blue racers that were recorded on more than one occasion were rarely
caught again at the original location. For different individuals,
distances between capture points ranged from zero up to a little more
than three-fourths of a mile. The area of concentrated study was a
mile and a half in greatest diameter; there was scant opportunity for
capturing racers that moved greater distances. Even those that moved
as far as a mile would have passed beyond the boundaries of the study
area in most instances. Many of the marked racers that disappeared
from my records probably moved beyond the limits of the study area.
Nevertheless, in the great majority of instances, the distances
between successive capture points for the same individual were
relatively short, indicating that each racer tends to remain
permanently in a restricted area.
Most captures were made in the type of grassland or brush that
provides favorable habitat for the racer during the season of
activity, but many other captures were made in woodland along the
rock ledges where the snakes come to hibernate. Four different types
of movement may be recognized: 1) those in the rock ledge area where
hibernation occurs; 2) those between the area where the summer is
spent and the hibernation ledge--an actual small scale seasonal
migration which takes place in spring and autumn--3) those within a
home range, which are part of the day-to-day activities of the racer,
and, 4) wandering movements by which the racer shifts its activities,
perhaps permanently, from one area to another. In the records of any
one snake these different types of movements cannot always be sorted
with certainty. Each type will be discussed separately.
Relatively few movements along the ledges were recorded. It seems that
having migrated to a ledge, the racer promptly finds its hibernaculum
and retires for the winter. In spring there is equally prompt
scattering of the emerging racers, which no longer find the ledge
attractive. Most recorded movements along the ledges were short. Of 76
movements, nine exceeded 1000 feet, and only four others exceeded 500
feet. Most of the shorter movements were recorded within an autumn
season, but several were recorded after the lapse of one or more
seasons of activity. The longer movements were as follows: 1250 feet
after 8 seasons (male); 1300 feet after three seasons (female); 1600
feet after one season (female); 2000 feet after one season (female);
2280 feet after seven seasons (male); 2200 feet in same season
(female); 2410, 2600, and 3200 feet, each after one season (all
males). The trend of these records suggests that the tendency to
return year after year to the same hibernaculum is not strong; after
using one for a period of years, the racer may abandon the stretch of
ledge and, starting out in the opposite direction from its summer
range, find a new hibernaculum as much as half a mile from the old
one. Records of distances between capture points on the ledges for
individual racers are shown in Fig. 12.
A total of 124 movements between summer ranges and ledges were
recorded, and the distances averaged 1309 feet--approximately a
quarter mile. Some racers living in hilltop fields may have had home
ranges that included rock ledges, or at least were adjacent to them.
In such instances no seasonal migrations would have been necessary to
reach hibernacula in the autumn and summer ranges in the spring.
Several short movements--100 feet, 150 feet, and 200 feet--can be
explained on the basis that home ranges and hibernation ledges
overlapped or were near at hand, but most of the movements were
longer. The longest movement was 4020 feet, after a lapse of four
seasons. Twenty-four movements exceeding 2000 feet were recorded. For
these the intervals between captures averaged more than double the
time for the remaining movements, indicating that the longtime
permanent shifts were involved in many instances.
[Illustration: Fig. 9. Histogram of movements of blue racers between
hilltop rock outcrops used for hibernation, and summer habitat on the
Reservation and Rockefeller Tract. Movements of females tend to be
somewhat shorter than those of males.]
For all the racers living in bottomland, ranges were separated from
ledges by areas of wooded hillsides averaging approximately 700 feet
across. These relatively unfavorable areas had to be traversed in the
course of the semi-annual migrations. Even some of the racers that
lived in hilltop fields apparently crossed wooded slopes in order to
reach distant hibernation ledges, or else each reached the ledge by a
roundabout route although it could have found a ledge much nearer its
summer range. For the 124 ledge-to-field and field-to-ledge movements,
the median distance was 1030 feet. The sexes were almost equally
represented in this sample but the average distance for the 55
males--1425 feet--notably exceeded that for the 69 females--1220 feet.
These movements are shown in Fig. 9.
McCauley (1945:76) in Maryland described what seemed to be incipient
territoriality in a large male racer that remained several hours in a
small area, crawling about conspicuously with head raised, seemingly
on patrol. When an even larger male racer intruded, the first one
aggressively drove him away, but neither paid any attention to a king
snake that was also on the area. Other authors have noted the
attachment of a racer to a small familiar area. Conant (1938:53) wrote
that many of the racers he saw sought shelter in definite retreats.
One of these racers was seen resting on top of a brush pile four times
in a single afternoon, and each time it followed the same route to the
same inaccessible spot beneath the brush.
My own observations do not bear out the idea that racers maintain
regular territories, since several males may be present within a small
area, even in the breeding season. Hostile behavior between males has
not been observed by me under natural conditions, and in confinement
has been seen only in instances of self defense. Like the racer Conant
observed on a brush pile, individuals may linger in the vicinity of a
favored shelter or foraging area for periods of hours, but such
associations are ephemeral, and soon the snake moves on. In a
uniformly favorable habitat a racer may cruise about freely in tall
grass or brush. Individuals that I have attempted to follow, after
flushing them or releasing them from traps, often covered distances of
100 to 300 feet within periods of a few minutes before I lost them. In
such instances I maintained sufficient distance between myself and the
snake so that the latter was not actively escaping. Probably the snake
was not aware of pursuit in most instances, although I was able to
glimpse it through the stems of grass, weeds, or shrubs, or was
informed of its course by the swaying tops of grass and other
vegetation.
For many of the racers captured over periods of years it was possible
to plot "minimum home ranges" in the areas that they occupied. One
caught 12 times in five consecutive years will serve as a typical
example. There were seven locations involved; three captures were made
at one point and two captures at each of two others; the other five
locations were each represented by a single capture. One of the seven
locations was for a capture made at a rock ledge in October, and hence
can be eliminated from considerations of home range. The other six
locations are based upon captures made from late May to early August,
and they form a rhomboid pattern, with three locations in alignment on
one side and two others inside the quadrangular figure formed by the
five outlying points. Obviously such a group of records gives some
idea of the location and extent of the snake's activities but the
information is far from complete. As shown by Odum and Kuenzler
(1955), a much larger series of records, usually several dozen, with
eight or more marginal locations, is necessary to illustrate even an
approximation of the actual home range. Under the conditions of my
study such a series of records was unattainable. Few if any of the
racers recaptured had more complete series of records than the one
mentioned above.
For 20 racers the records were sufficiently numerous and well
distributed to permit plotting of minimum home ranges. One of these
ranges was hexagonal, nine were pentagonal, eight were rhomboidal and
three were triangles. In four instances the area encompassed was
broken by woodland, indicating that the home range comprised two or
three disjunct segments. In all instances the smaller segments were
triangular. The 20 minimum home ranges averaged 6.6 acres (3.2 to
12.8). The 15 ranges of males averaged 7.3 acres, whereas the five
ranges of females averaged only 4.5 acres, but the sample is too small
to be relied upon for differences in the sexes.
[Illustration: Fig. 10. Movements of blue racers within or between
areas of summer habitat on the Reservation and Rockefeller Tract. The
trends are much alike for males and females.]
In an earlier publication (Fitch, 1958:73) I discussed an alternative
method for determining size of home range in animals that move about
freely within a chosen area, not having their movements restricted by
attachment to a specific home base. Ordinarily any two records of the
animal within its home range will be separated _on the average_ by a
distance equal to half the diameter of the area. Assuming that home
ranges in general tend to have a circular shape, except as restricted
by limiting environmental factors, the area can be easily computed
from the average recorded movement--the home range radius. It is
necessary, of course, to have a sufficiently large number of records
of movements to obtain an average that is statistically reliable.
A major problem is that of recognizing movements that involve an
extension of the original range or a shift away from it to a new area.
A few exceptionally long movements were recorded. If these are
included in the computations of home range, they greatly increase the
average distance, probably introducing error. Also, the number of
exceptionally short movements was greater than might have been
expected if all locations of capture are at random to each other. In
some instances a racer newly released may have blundered into the same
trap again, or into the trap at the opposite end of its drift fence.
In other instances traps may have been so strategically situated with
respect to preferred travel routes that they caught the same snakes
repeatedly. In still other instances, the range of an individual might
have been mostly outside the study area, with only one end or corner
overlapping the trap sites.
A total of 471 records for consecutive captures in field areas is
available, 305 for males and 166 for females. In 20 instances
successive sites of capture were the same and movement was recorded as
zero. Of the 471 records, 207 involved a relatively long time span,
including at least one hibernation period; the remaining 264 were
based upon successive records within the same season of activity. The
trends were much the same in the records involving a longer time span
(up to four years) as in those records involving captures made in a
single season, but for the longer periods there were some
exceptionally long movements, and relatively few short movements of
less than 100 feet.
Records of male racers and those of females were used for separate
computations. For each series, the ten per cent of movements that were
longest and the ten per cent that were shortest were eliminated from
consideration in calculation of the average distance between points of
capture. For the remaining 244 records of males an average movement of
595 feet was calculated, and for 132 records of females an average
movement of 574 feet. These distances, if accepted as typical home
range radii, would represent home ranges of 26.3 acres for males and
23.8 for females. In an earlier discussion of spatial relationships in
the racer (Fitch, 1958:119), based upon relatively scanty data, I
estimated the home range to be approximately 23 acres in males. But
with only nine records for female racers I calculated the home range
to be 9.7 acres.
The disparate figures obtained from plotting minimum home range and
from calculating average home range radius are not irreconcilable,
since a minimum home range based on only four or five points would
ordinarily include only a fraction of the actual range. Distances up
to 1500 feet are included in the calculation of home range. It seems
that home ranges often have a diameter of this magnitude or a little
larger, although the estimated average diameter is 1140 feet. Home
ranges probably most often deviate from circular shape to form an
ellipse, with one diameter markedly exceeding the other. Woodland,
water, roads, buildings, or cultivated fields, or other areas that are
unfavorable or uninhabitable often form the boundary of a home range
and influence its shape.
Many of the longer movements constituted clear-cut shifts in range. In
one exceptional instance a large adult female captured in the
northeastern part of the Reservation on June 22, 1950, was released 21
days later at a point 3900 feet southwest of the place of capture. On
May 27, 1960 she was caught within 600 feet of the original location,
seemingly having made a homing movement. Among the nine racers
recorded to have made longest movements (exclusive of those movements
made to or from hibernacula) four were recorded also to have made
later long movements in the reverse direction, probably returning,
each to its original home range, although in every instance the return
movement was somewhat less than the original. A female of two-year-old
size when first captured on September 2, 1957, was recaptured 3100
feet southeast on May 10, 1958. On August 7, 1959, she was recaptured
again 2400 feet from the second location in the direction of the
original capture. Similarly, in a three-year-old female a shift of
2730 feet was recorded at the second capture after 21 months, and at
the third capture 14 months after the second, a return trip of 2360
feet had been made. A second-year female made a trip of 2640 feet
between May 17 and October 1, 1960; by May 1961 she had returned 2000
feet to the vicinity of her original capture. From one year to the
next an adult male shifted 2450 feet; after another year he had moved
back 1550 feet. Most of the longer movements recorded were those
between home ranges in fields and hibernacula along ledges, but in
this class of movements, distance was somewhat proportional to elapsed
time. For 59 such movements exceeding 2000 feet the average was 3.1
years, whereas for 114 field-to-ledge movements of less than 2000
feet, average elapsed time was 1.6 years. This trend suggests that
over periods of years a racer is likely to shift its range or its
hibernaculum or both.
[Illustration: Fig. 11. Map showing home ranges of five blue racers,
as indicated by numerous captures in successive summers, in small
valley where Reservation headquarters are located, and spatial
relations of their hibernacula, as represented by points of capture
along hilltop limestone outcrops. In spring and autumn, traveling to
and from hibernacula, the snakes migrate across wooded slopes. Each
"minimum home range" is enclosed in a dotted line, and a distinctive
symbol is used to show successive points of capture for each snake.]
[Illustration: Fig. 12. Map of 600-acre area of Reservation and
Rockefeller Tract, including parts where field study was most
concentrated, showing movements of the 20 blue racers recorded to have
shifted over the longest distances. The figure following the sex sign
of each individual indicates number of months elapsed between the
captures at the localities represented by the dots.]
Average elapsed time between captures was 7.7 months. In the 471
field-to-field movements recorded, 53--slightly more than eleven per
cent--exceeded 1500 feet and can reasonably be considered shifts of
home range. The average elapsed time between captures for this group
of snakes was 9.5 months. The evidence suggests that, even in an area
of favorable habitat, somewhat more than ten per cent of the racers in
a population annually shift their home ranges somewhat, but that many
stay in the same home range for periods of years or perhaps throughout
life.
Shifts in range were especially noticeable where availability of
suitable habitat underwent seasonal change. Along the north edge of
the Reservation, prairie adjoined cultivated fields where grain or hay
was grown. Until late May, the cultivated crops made little growth and
the fields were almost bare. They provided insufficient shelter for
the racers, which tended to keep to the prairie, where old grass of
the previous year's growth furnished them with ample cover. Later in
the season, crops, of oats, wheat, and alfalfa constituted suitable
cover for the racers, and many of them shifted their ranges to the
cultivated fields, but corn and milo crops were much less adequate for
their needs. After harvesting of crops, cover in the fields was again
inadequate for the racers' needs, and they tended to retreat to edge
situations, or to adjacent prairie.
Food Habits
_Methods of Obtaining Prey_
The racer hunts by stealth, but actively, obtaining its prey by keen
eyesight and swift movements. Wright and Bishop (1915:160) wrote that
because of its great speed it can catch anything that moves on the
ground. As a racer moves stealthily through dense vegetation, its
dull, uniform dorsal color blends well with the surface litter of dead
plant material. In prowling, the snake glides along rapidly and
alertly, in a jerky fashion, with frequent momentary pauses and
changes of direction. Because of its inconspicuousness, it is not
likely to be detected by the prey until it is close at hand. The snake
is ready to dash in pursuit of any small animal that flies, jumps or
runs to escape.
On August 27, 1955, my daughter observed a large racer hunting among
tall weeds at the edge of the pond on the Reservation. Several times
in the course of its movements, it flushed small frogs (_Rana
pipiens_) and each time the snake darted in unsuccessful pursuit of
the rapidly hopping frog. On several occasions I have been led to a
blue racer by the distressed croaking of a frog that the snake had
captured. In each instance, despite my cautious approach, the racer
saw me before I detected it, and then darted away, abandoning its
prey. On one occasion, while I was still a few yards from the racer,
and before the latter had detected me, the frog broke free and hopped
away rapidly through tall grass and weeds, and after several leaps,
hid, concealed by dense screening vegetation. The racer darted in
pursuit but could not find the frog. For several minutes the snake
persisted in an active search; with forebody elevated and head held
high, it would turn first in one direction and then in another, with
nervous, jerky movements, obviously keyed up to a high pitch of
excitement. Then it became aware of my presence, lowered its head, and
glided away rapidly, abandoning the search.
Although the racer depends to a large extent on sight to find its
prey, scent may play some part also, as indicated by the presence in
the food of young mammals taken from nests, some probably found
underground. Near Garnett, Kansas, on May 4, 1952, Richard B. Loomis
found a racer attacking a collared lizard (_Crotaphytus collaris_)
beneath a large flat rock. The lizard was retaliating by biting the
snake's neck. The posterior part of the snake protruded into the open,
and its thrashing had directed the attention of the observer to it.
Whether the racer first found the lizard under the rock, or followed
it there after flushing it in the open is unknown.
An encounter between a large blue racer and an adult Great Plains
skink (_Eumeces obsoletus_) on August 30, 1948, was described as
follows: "The skink, grasped by one flank, had twisted back and seized
the skin of the snake's neck in a bulldog grip, and they lay
interlocked, motionless except for their rapid panting, and occasional
straining of the skink to bite harder or of the snake to shift its
grip and work its jaws toward the skink's head. The racer broke the
skink's grip, and began to swallow it head first. When only the hind
legs and tail of the skink still protruded from the racer's mouth, I
lunged forward in an attempt to catch both reptiles. With a sudden
movement the snake disgorged the skink, which darted away into the
grass and escaped" (Fitch, 1955:78).
_Composition of Food_
Many authors have contributed to knowledge of the racer's food habits.
In most instances the records have been few or casual, but several
intensive studies have been made, notably by Surface (1906) in
Pennsylvania, Ortenburger (1928) for the species as a whole, Uhler,
Cottam and Clark (1939) in Virginia, Clark (1949) in Louisiana,
Auffenberg (1949) in southern Texas, Hamilton and Pollack (1956) in
Georgia, and Klimstra (1959) in southern Illinois. However, the
findings of different authors are not strictly comparable; some have
made general statements concerning the food habits but have mentioned
specific items only when these were considered unusual. Certain
authors have listed individual prey animals eaten; others have
indicated the percentages (in bulk or in frequency) that the different
kinds of prey comprised. Some writers have identified food animals
only in broad categories such as "insect," "beetle" or "snake" while
others have undertaken specific determinations for all the prey or for
certain taxonomic groupings that were subjects of special interest.
For the eastern black racer (_C. c. constrictor_) the following food
items have been recorded: 1 robin (_Turdus migratorius_, Storer,
1839:226); 1 copperhead (_Agkistrodon contortrix_, Verrill,
1869:158); 1 weasel (_Mustela_ sp.--presumably the diminutive
_M. rixosa_--Atkinson, 1901:148); 3 undetermined mammals, 1 rabbit,
1 undetermined mouse, 7 voles (2 _Microtus_ sp., 4 _M. pennsylvanicus_,
1 _Clethrionomys gapperi_), 1 undetermined bird, 2 robin eggs, 2
garter snakes (_Thamnophis sirtalis_), 1 water snake (_Natrix
sipedon_), 1 grass snake (_Opheodrys vernalis_), 1 green frog (_Rana
clamitans_), 1 wood frog (_R. sylvatica_), 1 grasshopper (_Melanoplus
femur-rubrum_) 2 camel crickets (_Ceuthophilus_ sp.), 5 moths
(cecropia, regal, imperial), 4 beetles, 1 currant worm, 1 ichneumonid
wasp (_Nematus ribesii_), 1 currant worm (Surface, 1906:170); 1 ribbon
snake (_Thamnophis sauritus_, Ditmars, 1907:282); 3 snakes (1
_Liopeltis vernalis_, 1 _Storeria occipitomaculata_, 1 undetermined),
6 white-footed mice (1 _Peromyscus leucopus_, 5 _P. nuttalli_), 1 vole
(_Microtus pennsylvanicus_), 16 crickets (9 _Gryllus pennsylvanicus_,
4 _G. assimilis_, 2 _Miogryllus verticalis_, 1 _Nemobius fasciatus_),
2 grasshoppers (_Dissosteira_ sp.), 1 lepidopteran, 3 elaterid beetles
(Ortenburger, 1928:200). Richmond and Goin (1938:310) recorded
finding the stomach of a black racer crammed with June beetles
(_Phyllophaga_). Conant (1938:53) recorded a black racer from Ohio
that had a smaller individual of its own species in its stomach. The
smaller snake contained a caterpillar. Uhler, Cottam and Clark
(1939:34) found food in 16 of 34 black racers from Virginia. Mammals,
including a shrew (_Blarina brevicauda_), a mole, a flying squirrel
(_Glaucomys volans_), a microtine, and a mouse (_Peromyscus_ sp.) made
up 26 per cent, 2 worm snakes (_Carphophis amoenus_), 2 ring-necked
snakes (_Diadophis punctatus_), and 1 water snake (_Natrix sipedon_)
made up 25.6 per cent, 5 birds including a warbler and a sparrow, made
up 17.75 per cent; 2 frogs (_Rana_ sp.) made up 9.38 per cent, 1 fence
lizard (_Sceloporus undulatus_) made up 6.25 per cent, and insects,
including cicadas (_Tibicen_ sp.) and larval lepidopterans, made up
15.09 per cent. In Indiana, Minton (1944:457) examined 11
food-containing stomachs; there were rodents in six, snakes in five, a
tree frog in one, and insects (cicadas, large grasshoppers) in four,
and another black racer was found swallowing a small box turtle
(_Terrapene carolina_). In Maryland, McCauley (1945:75) examined eight
digestive tracts and recorded a shrew (_Blarina brevicauda_) in one,
an unidentified mammal in one, 2 small cicadas in one, 2 small
chickens in one, a fence lizard (_Sceloporus undulatus_) in one, and
frogs and toads (including _Hyla crucifer_) in one; a ninth snake had
eaten a half grown rat. In Connecticut, Finneran (1948:124) observed a
large black racer eating a 21-inch garter snake (_Thamnophis
sirtalis_). Duellman (1951:338) recorded a black racer in Greene
County, Ohio, swallowing a large garter snake (_Thamnophis sirtalis_).
In Kentucky, Barbour (1950:104) recorded remains of an unidentified
snake in one stomach.
Many authors likewise have recorded food of the southern black racer
(_C. c. priapus_). In Georgia, Wright and Bishop (1915:160) recorded
finding 2 racerunners (_Cnemidophorus sexlineatus_), a skink
(_Lygosoma laterale_), 4 green tree frogs (_Hyla cinerea_) and 1 pine
woods tree frog (_H. femoralis_) in stomachs. They also stated that
the toad (_Bufo lentiginosus_ [= _terrestris_]) was the most important
article of food. Burt and Hoyle (1934:205) wrote that a racer from
Rogers County, Oklahoma, had eaten an adult male collared lizard
(_Crotaphytus collaris_). In Florida, Carr (1950:80) found one of
these black racers eating a leopard frog (_Rana pipiens_). Hamilton
and Pollack (1956:523) examined digestive tracts of 62 and found food
in 57, comprising the following percentages by volume: _Lygosoma
laterale_, 34.2; _Eumeces fasciatus_ and _E. egregius_, 11.3;
_Cnemidophorus sexlineatus_, 8.8; _Sceloporus undulatus_, 3.5;
undetermined lizard, 3.5; _Opheodrys aestivus_, 6.6; _Diadophis
punctatus_, 3.1; _Storeria dekayi_, 1.6; _Coluber constrictor_, 1.8;
_Heterodon platyrhinos_, 1.8; _Masticophis flagellum_, 1.8; _Rana_
sp., 5.3; _Hyla cinerea_, 1.8; _Hyla versicolor_, 1.8; _Peromyscus_,
1.8; undetermined rodent, 1.8; lepidopterous larva, 1.7.
In southern Illinois in an intergrading population of racers
intermediate between _C. c. priapus_ and _C. c. flaviventris_, Cagle
(1942:188) examined several stomachs and found 1 chipmunk (_Tamias
striatus_), 2 voles (_Microtus_ sp.), 2 mice (_Peromyscus_ sp.), 2
green snakes (_Opheodrys_ sp.), 1 water snake (_Natrix sipedon_) and
grasshoppers. From this same population Klimstra (1959:212) examined
137 digestive tracts of which 115 contained food as follows: 194
locustids, 118 gryllids, 17 undetermined beetles, 13 carabids, 6
scarabaeids, 10 lepidopterans, 9 hemipterans, 1 hymenopteran, 2
homopterans, 1 dipteran, 17 undetermined insects, 73 _Peromyscus_ sp.,
19 _Microtus ochrogaster_, 9 _M. pinetorum_, 12 _Sylvilagus
floridanus_, 3 _Scalopus aquaticus_, 3 _Rattus norvegicus_, 4 _Mus
musculus_, 2 _Tamias striatus_, 2 _Synaptomys cooperi_, 16 _Rana
pipiens_, 8 _Acris crepitans_, 2 _Rana clamitans_, 2 _R. palustris_, 1
_R. catesbeiana_, 4 _Hyla crucifer_, 3 _Pseudacris nigrita_, 4
_Lampropeltis calligaster_, 4 _Sceloporus undulatus_, 4 _Chrysemys
picta_, 1 _Heterodon platyrhinos_, 1 unidentified reptile, 4
_Sturnella magna_, 1 _Otocoris alpestris_, 4 unidentified birds.
Percentages by volume of the various categories in this sample were:
insects, 39.1; mammals, 32.9; amphibians, 10.8; reptiles, 8.3; birds,
6.3; miscellaneous, 2.6.
Food of the "buttermilk snake" (_C. c. anthicus_) is known only
through Clark's study (1949:249). In an unstated number of
examinations he found "mice" in 25, "rats" in five, lizards
(_Sceloporus undulatus_ and perhaps others) in eight, frogs (_Rana
pipiens_) in seven, and birds in three.
The food of _C. c. stejnegerianus_ is known only from the work of
Auffenberg (1949) but his sample was based on 206 racers that had
food, among the total of 291 recorded. Unfortunately, he did not
present actual numbers of the various prey animals, but divided the
food into seven categories and listed these as percentages. He did not
indicate whether the percentages represented volumes or numbers of
individual occurrences, and evidently there was some error in
computation since his combined percentages totalled 111. The
categories and their percentages were as follows: grasshoppers, 42.5;
crickets, 13.5; miscellaneous insects, .6; earless lizards
(_Holbrookia_ sp.), 40.1; scaly lizards (_Sceloporus_ sp.) 2.1; frogs
(_Rana_ sp.) 10.0; rodents, 2.2. Auffenberg divided his sample of
racers into five size classes, and showed that the smaller snakes fed
chiefly on insects whereas vertebrates were increasingly prominent in
the food of the larger snakes.
The food of _C. c. mormon_ is known chiefly through the work of
Ortenburger (1928:228) who cited instances of a skink (_Eumeces
skiltonianus_) and a young garter snake (_Thamnophis sirtalis_) being
eaten, and listed the following items from 24 stomachs that he
examined: 7 decticids, 8 acridids, 5 oedipines, 1 tryxaline, 6
_Melanoplus_ sp., 3 _M. mexicanus_, 2 _M. devastator_, 1 _M.
bivittatus_, 2 _Dissosteira carolina_, 1 _Chortophaga viridis_, 3
_Neduba carinata_, 3 _Trimerotropus_ sp., 7 _Hippiscus_ sp., 2
_Steiroxys_ sp., 3 _Canoula pellucida_, 2 _Stenopelmatus fuscus_, 2
_S. pictus_, 4 _Gryllus assimilis_, 4 _Ceuthophilus_ sp., 1
_Pristoceuthophilus pacificus_, 6 _Gammarotettix bilobatus_ and 2
cicada nymphs. Grinnell, Dixon and Linsdale (1930:149) found that one
of these racers had eaten a cricket. Fitch (1936:644) found another in
the act of swallowing an adult vole (_Microtus californicus_), and
recorded (1935:18) that two alligator lizards (_Gerrhonotus
multicarinatus_) were found in the stomach of still another. Woodbury
(1931:75) recorded that a racer from Utah had a sagebrush scaly lizard
(_Sceloporus graciosus_) in its stomach. Of the specimens examined in
the University of California Museum of Vertebrate Zoology, no. 17256
from the Mad River, Trinity County, California, had eaten an alligator
lizard (_Gerrhonotus coeruleus_), and no. 10120 from Yolla Bolly
Mountain in the same county had eaten a bird (unidentified) and a
Jerusalem cricket (_Stenopelmatus_ sp.).
Several authors have published specific information regarding the food
of _C. c. flaviventris_. Hurter (1911:171) caught a blue racer in the
act of swallowing a copperhead (_Agkistrodon contortrix_). Taylor
(1892:331) recorded finding garter snakes in several large racers.
Pope and Dickinson (1928:53) recorded instances of blue racers feeding
on racerunners (_Cnemidophorus sexlineatus_). Ortenburger (1928:181)
examined 22 stomachs and recorded: 1 large garter snake (_Thamnophis
sirtalis_), 1 vole (_Microtus pennsylvanicus_), 1 frog (_Rana_ sp.),
31 crickets (_Gryllus assimilis_), 4 decticines, 2 acridids,
grasshoppers (1 _Hippiscus_, 2 _Melanoplus_ sp., 1 _M. confusus_, 1
_M. differentialis_, 1 _Dissosteira carolina_, 1 _Sphargemon collare_,
1 _Trimerotropus_ sp., 1 _Orphulella_ sp., 1 _Chloealtis conspersa_, 1
_Chortophaga viridifasciata_, 1 _Omaseus_ sp., 1 _Pedocetes_ sp.), and
2 caterpillars (1 noctuid, 1 sphingid). Gloyd (1928:123) recorded a
hatchling glass lizard (_Ophisaurus attenuatus_) in the stomach of a
juvenal racer. Force (1930:31) found a racer eating eggs from the nest
of a cardinal (_Richmondena cardinalis_) and another racer eating eggs
of a red-wing (_Agelaius phoeniceus_). Gloyd (1932:403) recorded an
observation of a racer overpowering and swallowing a copperhead.
Anderson (1942:210) recorded remains of crickets and grasshoppers in
feces. Hudson (1942:55) recorded a racerunner (_Cnemidophorus
sexlineatus_) in the stomach of a juvenile and recorded an earless
lizard (_Holbrookia maculata_) 3 lizard eggs, and 14 grasshoppers
(_Melanoplus differentialis_ and others) in the stomach of another.
Marr (1944:484) found a harvest mouse (_Reithrodontomys montanus_) in
one. Breckenridge (1944:118) recorded stomach contents including a
garter snake (_Thamnophis sirtalis_), a frog (_Rana pipiens_), 3
crickets and 2 moths. Mossimann and Rabb (1952:27) recorded that a
racer disgorged several grasshoppers. Fouquette and Lindsay
(1955:411) recorded that a blue racer had eaten a harvest mouse
(_Reithrodontomys_ sp.). Carpenter (1958:114) recorded that one blue
racer had eaten a green snake (_Opheodrys aestivus_) and another had
eaten a grasshopper and a camel cricket.
Even though the sets of data cited above are not entirely comparable,
certain trends are evident. The black racers of the eastern states
(especially _C. c. constrictor_ of more northern regions) take a high
proportion of vertebrates in their prey. Among these vertebrates
snakes especially are well represented and the black snake would seem
to be of some importance as an ophiphagous predator. The birds and
mammals taken include some that are bulky (robin, cottontail, and even
a weasel--the most formidable prey eaten). Presumably the rabbits that
were eaten were young. In samples from the eastern United States
insects made up small to insignificant parts of the food; they were
lacking entirely or at least were not mentioned in the samples
examined by McCauley and Wright and Bishop. In the blue racer of the
central states, insects (mostly grasshoppers and crickets) are much
more prominent in the food and vertebrates correspondingly less
prominent. The vertebrates eaten are largely lizards, small snakes and
mice. _C. c. stejnegerianus_ is much like _flaviventris_ in the trend
of its feeding. _C. c. mormon_ is less known than these subspecies in
its feeding, but indications are that it takes a higher proportion of
orthopteran insects and smaller proportions of mammals and snakes than
do any of the other subspecies.
In my own field study a total of 1357 food records were accumulated,
one of the largest samples known for any kind of snake. Most of these
records were from the small area where my population study was carried
on, and studies of other kinds of animals, including those that were
the racer's prey, were simultaneously in progress. Because large
collections of reference materials were available, it was possible to
identify to species many of the prey items found, even though they
were incomplete and highly fragmented because most of them were
recovered from fecal material.
The prey is, of course, swallowed entire, and the recently swallowed
items squeezed from the stomachs provide the best material for the
study of food habits. However, relatively few racers had detectable
food items in their stomachs; digestion is rapid and often the snake
was in a trap for a day or more before it was found. Therefore the
greater number of records were obtained from scats. The residue in
scats consisted entirely of hard and indigestible parts such as the
chitin of insects' exoskeletons and the hair, feathers, scales, teeth
and occasional bone fragments of the vertebrate prey. The insects
eaten could usually be counted individually by sorting parts, such as
heads or hind legs. With mammals, birds and reptiles the hair,
feathers, or scales did not permit counting of individuals--each
occurrence was assumed to represent one individual but in some
instances two or more may have been present. Amphibians, lacking
indigestible dermal structures were in most instances not represented
at all in the scats, since their tissues were more or less completely
dissolved by the digestion of the snakes. Soft-bodied larvae of
insects and other invertebrates conceivably could be likewise
completely digested, but such occurrences must be rare, as most of the
invertebrates known to be eaten have the mouth parts, at least,
heavily chitinized.
Admittedly the factors discussed above would cause some bias in the
percentage composition of the food determined from scats, but I
believe that the amount of error introduced was slight, because,
judging from the records of items from stomachs, amphibians are not
eaten frequently, and even mammals are not eaten frequently enough so
that there is much chance of a snake taking two or more individuals at
the same meal, unless it is robbing a nest containing a litter of
young.
[Illustration: Fig. 13. Diagram showing percentage frequency of
occurrence of various categories of prey in a sample of 1008 food
items identified from scats and stomachs of blue racers from the
Reservation and Rockefeller Tract. Insects, especially, orthopterans,
made up the great majority of prey items taken.]
The largest sample, based on 1008 food items, was obtained from 479
scats collected from the Reservation and Rockefeller Tract over the
period 1949 through 1961. Items recorded were: 183 gryllid crickets
(144 _Gryllus assimilis_, 36 _Gryllus_ sp., 3 unspecified); 353
locustid grasshoppers (41 unspecified, 73 _Arphia simplex_, 67
_Melanoplus femur-rubrum_, 66 _M. bivittatus_, 39 _M. differentialis_,
17 _Melanoplus_ sp., 15 _Dissosteira carolina_, 8 _Chortophaga
viridifasciata_, 6 _Syrbula admirabilis_, 6 _Sphargemon equale_, 2
_Melanoplus scudderi_, 2 _Schistocerca obscura_, 1 _S. americana_);
94 camel crickets (_Ceuthophilus_ sp.), 93 katydids (36
_Neoconocephalus robustus_, 15 _Orchelimum vulgare_, 15 _O. nigripes_,
6 _Conocephalus_ sp., 4 _Orchelimum_ sp., 2 _Amblycorypha inasteca_,
1 _Neoconocephalus_ sp., 1 _Daihinia brevipes_); 7 cicadas (5 _Tibicen_
sp., 1 _T. pruinosa_, 1 _T. lyrica_); 45 unidentified insects; 17
beetles (including 1 _Phyllophaga_, 1 _Calosoma scrutator_, and 2
other carabids); 2 noctuid moths (_Mocis latipes_) and 1 caterpillar;
2 homopterans, 1 bee, 1 ant, 1 spider; 69 voles (59 _Microtus
ochrogaster_, 9 _Microtus_ sp., 1 _M. pinetorum_); 31 white-footed
mice (15 _Peromyscus leucopus_, 14 _Peromyscus_ sp., 1 _P.
maniculatus_); 36 miscellaneous small mammals (6 _Cryptotis parva_, 4
_Sigmodon hispidus_, 4 _Reithrodontomys megalotis_, 3 _Blarina
brevicauda_, 2 each of _Scalopus aquaticus_, _Sylvilagus floridanus_,
and 1 unspecified shrew); 50 snakes (16 _Coluber constrictor_, 15
_Diadophis punctatus_, 14 _Thamnophis sirtalis_, 4 _Elaphe obsoleta_,
1 _Natrix sipedon_); 7 lizards (5 _Eumeces fasciatus_, 1 _E._
_obsoletus_, 1 _Cnemidophorus sexlineatus_); 3 unspecified "reptiles";
5 birds (none identified to genus); 3 bird eggs, 1 narrow-mouthed toad
(_Gastrophryne olivacea_).
[Illustration: Fig. 14. Diagram showing estimated percentage by weight
of various categories of prey in a sample of 1351 items, including all
those represented in Fig. 13 and others from various parts of Kansas.
Since the vertebrate items are on the average much bulkier than the
insects eaten, vertebrates comprise most of the food, even though
insects are eaten in much larger numbers.]
[Illustration: Fig. 15. Diagram showing estimated percentages by
weight of various categories of prey in a sample of 69 food items
squeezed out of stomachs of the blue racers captured at Harvey
County Park. Most of the items were vertebrates, and lizards
(_Cnemidophorus_) were especially prominent in the food at this
locality. Samples of prey from scats (included in Figs. 13 and 14) and
from stomachs show somewhat different trends, and neither is entirely
representative of the actual feeding. Also, local differences in food
sources are important.]
Over the same period that the sample of scats was collected, a much
smaller food sample of 73 prey items was collected by squeezing
recently eaten food from the racers' stomachs, or by finding the
snakes actually swallowing their prey. These items from stomachs are
listed separately because they include relatively more vertebrates
than do the items from scats. A grasshopper or cricket eaten by a
large racer might have passed undetected, while a relatively large
item such as a vole or lizard would have produced a conspicuous bulge
in the snake that ate it, and would have excited the curiosity of the
investigator. A second difference is that the items from stomachs
included several frogs, whereas amphibians were absent from the much
larger sample from scats. A third difference is that the many insects
found in stomachs were all orthopterans with the exceptions of three
noctuid moths and the larva of a moth. Miscellaneous insects, such as
beetles, bees and ants recorded from scats were not found in stomachs.
Amphibians eaten are digested so completely that no recognizable parts
of them are to be found in scats, but remains of the insects
previously eaten by amphibians are to be seen in racers' scats. If not
recognized as secondary items, such remains might lead to erroneous
conclusions regarding the racer's food.
The items from stomachs were as follows: 21 grasshoppers (5 oedipines,
4 tryxalines, 5 _Melanoplus bivittatus_, 3 _M. differentialis_, 1 _M.
femur-rubrum_ and one each of _Chortophaga viridifasciata_,
_Dissosteira carolina_, and _Sphargemon equale_); 8 crickets
(_Gryllus_ sp.), 3 katydids, 3 camel crickets (_Ceuthophilus_ sp.), 3
noctuid moths, 1 larva of a moth; 10 voles (_Microtus ochrogaster_), 6
white-footed mice (5 _Peromyscus leucopus_ and 1 _P. maniculatus_), 4
harvest mice (_Reithrodontomys megalotis_); 1 shrew (_Cryptotis
parva_); 4 snakes (3 _Thamnophis sirtalis_, 1 _Storeria dekayi_); 4
lizards (2 _Eumeces obsoletus_, 1 _Cnemidophorus sexlineatus_, 1
_Ophisaurus attenuatus_); 4 frogs (_Rana pipiens_), 1 tree-frog (_Hyla
versicolor_).
Records from the Harvey County, Kansas study area include a series of
69 food items from 55 stomachs (of living snakes) and 210 food items
from 113 scats. There is a relatively high proportion of vertebrates,
including some frogs, in the stomachs, and with no frogs but more
miscellaneous insect material in the scats. But, for the sake of
brevity, the two categories of items are combined in the following
list: 55 grasshoppers (12 unspecified, 1 "locustid," 31 "oedipines," 7
"tryxalines," 5 "locustines," 2 _Melanoplus bivittatus_ and one each
of _M. femur-rubrum_, _M. scudderi_, _M. differentialis_, and _Arphia
simplex_); 48 crickets (31 _Gryllus assimilis_, 17 unspecified); 14
katydids (11 _Daihinia brevipes_, one each of rhadiphorine,
conocephaline and _Neoconocephalus_ sp.); 9 noctuid moths and 1 moth
larva; 26 miscellaneous insects (including 13 "beetles," 1 elaterid, 1
curculionid, 1 lygaeid bug, 1 ant, 1 wasp); 1 spider, 7 mice (5
_Peromyscus maniculatus_, 2 unspecified), 4 unidentified mammals, 1
vole (_Microtus ochrogaster_), 1 shrew (_Cryptotis parva_), 84 lizards
(77 _Cnemidophorus sexlineatus_, 6 _Sceloporus undulatus_, 1
unspecified), 6 snakes (4 "natricines," 1 _Thamnophis_ sp., 1
_Pituophis melanoleucus_), 1 "reptile," 1 "bird," 9 frogs (4
unspecified, 1 _Rana catesbeiana_, 4 _Rana pipiens_, 1 _Rana_ sp., 1
_Pseudacris triseriata_).
_Kinds of Prey_
Throughout the range of the racer small mammals make up an important
portion of the food, and the bulk of those eaten are voles (_Microtus_
sp.) and white-footed mice (_Peromyscus_ sp.). The voles being
diurnal, and having habitat preferences similar to those of the racer,
are especially subject to attack, but only large adult racers are
capable of swallowing a full grown vole. Probably most of the voles
eaten are immature. Of the white-footed mice, _P. maniculatus_
especially prefers a grassland habitat, and is usually found in
situations frequented by the racer. Being mainly nocturnal and
crepuscular, it is usually in hiding at times when the racer is
prowling, but may be flushed from its nest in a shallow burrow or
beneath a sheltering object, and overtaken by the snake. Other mammals
that are important in the food are harvest mice and other mice,
shrews, and young cottontails. The latter are small enough to be eaten
by racers only in the early stages of their life in the nest before
weaning. Rats (_Rattus_, _Sigmodon_), moles, sciurids, and weasels are
less frequent prey, ordinarily too large to be eaten by racers and
taken chiefly as defenseless juveniles.
Predation on birds is relatively uncommon, and in most instances it
involves the eggs or nestlings, or fledglings still slow and clumsy
and incapable of sustained flight, or, occasionally, injured adults.
Nests that are vulnerable are chiefly those of ground nesting species,
or of kinds that nest near the ground in grass or thickets. Many of
the birds recorded have not been identified to species, but those
identified have included a variety of small passerines and also
domestic chicks.
Lizards figure prominently in most of the food samples, but only a few
species, those that live on or near the ground in grassy places, have
been recorded. Most of the records pertain to scaly lizards
(_Sceloporus undulatus_ and _S. graciosus_), earless lizards (mainly
or entirely _Holbrookia maculata_), racerunners (_Cnemidophorus
sexlineatus_) and skinks (_Lygosoma laterale_ and _Eumeces_ sp.).
Snakes are important in the racer's food in most parts of the range,
but the large racers of the Northeast are those most inclined to
ophiphagous habits. The common garter snake (_Thamnophis sirtalis_) is
the species most commonly eaten. Probably this is a matter of
availability rather than preference, since the garter snake is one of
the commonest and most widely distributed of North American snakes,
occurring throughout most of the racer's range. The green snakes
(_Opheodrys_) also are represented frequently. The other snakes eaten
are mostly medium-sized to small colubrids, of a variety of kinds.
However, there are three records (from Connecticut, Missouri and
Kansas) of the racer preying on the venomous copperhead. There are
many records of the racer preying on smaller individuals of its own
species. In my own records racer remains appeared 18 times, equalling
in frequency those of the common garter snake and exceeding all other
kinds. In four of these instances the scale remains were relatively
few and the scales were relatively large, suggesting as an
alternative to actual predation that a racer may have eaten part of
its own sloughed skin, or that patches of shed skin may have adhered
to the scat after its deposition in the trap. However, in the
remaining 14 instances the remains of racer found in scats clearly
indicated cannibalism, since the scales found were small and numerous
and often were associated with bone. Cannibalism seems to occur
frequently enough to be a significant factor in the reduction of the
first year young. Liner (1949:230) described two instances of
cannibalism in a litter of blue racers hatched in captivity. In one
instance two young had seized the same lizard, and one having
swallowed the lizard, continued to engulf the other snake, although it
was of a size approximately equal to that of the first snake.
Nevertheless, swallowing was completed, with the snake eaten pressed
in a series of curves. A second instance of cannibalism occurred when
one young racer attempting to catch a lizard struck another racer by
mistake, then retained its hold and commenced swallowing. A similar
instance was observed in a brood that I kept in 1962 after hatching
had occurred in the laboratory.
Hatchling turtles of two kinds (_Chrysemys picta_, _Terrapene
carolina_) have been reported in the racer's food. Probably other
kinds are eaten also. However, the awkward shape and almost inflexible
shell of the prey on the one hand, and the slender form of the racer,
with limited distensibility of the gullet on the other, would limit
this type of predation to occasional instances involving an unusually
large racer and a small turtle.
There seem to be no records of the racer preying on salamanders. Many
kinds of frogs are eaten, chiefly ranids and hylids, and the leopard
frog (_Rana pipiens_) is the most frequent victim. Wright and Bishop
(1915:160) stated that the toad (_Bufo terrestris_) occupied first
place in the racer's food in the region of Okefinokee Swamp, Georgia,
but they mentioned no specific instances of this species being eaten.
Klimstra (_loc. cit._) found only four toads in his large sample of
digestive tracts from Illinois. Because of their virulent dermal
secretions, bufonid toads are avoided by many kinds of snakes and
predation on them by the racer probably is unusual.
Most authors who have written concerning the food habits of the racer
have mentioned insects as part of the diet. Statements in the
literature have often seemed to imply that the racer feeds on insects
in general, according to their availability. However, the large number
of records now available demonstrate that the racer is highly
selective in choice of its insect food, that soft-bodied orthopterans,
chiefly crickets, grasshoppers and katydids, are the usual insect
prey, with occasional predation on moths and their larvae. Eating of
other insects such as cicadas and June beetles, is a rarity, but on
occasion a racer may be tempted to sample such prey when it finds the
newly emerged imago before its exoskeleton has hardened. I am
convinced that such rarely occurring items as carabid beetles,
hemipterans, homopterans, diplopods and spiders are secondary prey
items, eaten by frogs that later were eaten by the snakes, in most
instances if not in all. It is noteworthy that several of the same
genera of grasshoppers and crickets are prominent in the food samples
collected in widely separated parts of the racer's range.
As might have been anticipated, different species of prey were not
utilized by the racers to the same extent throughout the snakes'
season of activity. Grasshoppers, for instance, fluctuated from a low
of 25.3 per cent (frequency) in the May sample to a high of 41.4 per
cent in the September sample. Availability of prey, rather than any
change of preference on the part of the racer, explains this trend.
Thus, the locust, _Arphia simplex_, which, unlike most local
grasshoppers, overwinters in the adult stage, is most prominent in the
food in May, represented by 15.7 per cent, but it decreases
progressively to a low of 1.8 per cent in September. The common
grasshoppers of the genus _Melanoplus_ show just the opposite trend,
increasing during the summer, from a low of 2.62 per cent in May (when
all are nymphs and most are too small to constitute a meal worthy of a
racer's attention) to a high of 31.5 per cent in September. Mammals
are best represented in the food in May, when they collectively
comprise nearly 30 per cent of the items taken, and they are
progressively less well represented as the summer advances. Both
_Microtus_ and _Peromyscus_ conform to this trend, but the relative
numbers of _Peromyscus_ rise again abruptly in October. The general
trend may be explained by the fact that in May most small mammal
populations have a high proportion of young of the year, and these
young are especially vulnerable to predation by the snakes. Also,
insects in general are less available in spring, and this may force
the racers to utilize vertebrates to a greater extent than at other
seasons. Actually, the seasonal changes in food sources are not
especially striking, and it seems that each important prey species is
utilized more or less throughout the season of the racer's activity.
Table 5. Distribution by Months of Various Categories of Prey Items
Recorded From Blue Racers From Kansas, Chiefly From the Reservation
and Rockefeller Tract
=======================+======+======+======+======+=======+======
| May | June | July | Aug. | Sept. | Oct.
-----------------------+------+------+------+------+-------+------
Cricket (233) | .17 | .37 | .28 | .01 | .05 | .12
_Ceuthophilus_ (94) | .01 | .19 | .30 | .14 | .13 | .23
Katydid (96) | .03 | .06 | .08 | .25 | .15 | .43
_Melanoplus_ (188) | .03 | .12 | .27 | .15 | .19 | .24
All grasshopper (388) | .15 | .17 | .21 | .16 | .12 | .19
_Microtus_ (79) | .45 | .32 | .13 | .02 | .07 | .01
_Peromyscus_ (39) | .41 | .18 | .08 | .08 | .05 | .20
All mammal (162) | .41 | .25 | .14 | .03 | .05 | .12
Lizard (70) | .07 | .46 | .29 | .15 | .01 | .02
Snake (61) | .37 | .18 | .08 | .13 | .09 | .15
_Arphia_ (72) | .50 | .25 | .12 | .04 | .03 | .06
-----------------------+------+------+------+------+-------+------
Table 6. Distribution of Various Common Prey Animals in a Sample of
625 Among Racers of Different Size Groups
====================+====================================================
| Snout-Vent Length (mm.) of Racers in Sample
Kinds of prey and +-----+-----+-----+-----+-----+-----+-----+-----+----
their percentage | 200 | 300 | 400 | 500 | 600 | 700 | 800 | 900 |1000
frequencies in | to | to | to | to | to | to | to | to | to
in samples | 299 | 399 | 499 | 599 | 699 | 799 | 899 | 999 |1099
--------------------+-----+-----+-----+-----+-----+-----+-----+-----+----
gryllid cricket | .40 | .39 | .11 | .25 | .23 | .15 | .15 | .12 | .08
| | | | | | | | |
_Melanoplus_ | | .09 | .14 | .14 | .14 | .15 | .20 | .27 | .25
| | | | | | | | |
_Ceuthophilus_ | .20 | | .11 | .13 | .06 | .07 | .12 | .09 | .04
| | | | | | | | |
_Orchelimum_ | | | | .04 | .02 | .01 | .01 | .01 |
| | | | | | | | |
tettigoniid | | | .03 | .02 | .06 | .03 | .02 | .05 |
| | | | | | | | |
"other grasshopper" | | | | | | | | |
and miscellaneous | | | | | | | | |
orthopteran | | .30 | .25 | .10 | .09 | .03 | .12 | .07 | .09
| | | | | | | | |
_Arphia simplex_ | | | .03 | .02 | .05 | .08 | .08 | .04 | .09
| | | | | | | | |
miscellaneous insect| | .04 | .04 | .09 | .07 | .04 | .08 | .05 | .04
| | | | | | | | |
lizard | .20 | .09 | .18 | .09 | .07 | .11 | .01 | .01 |
| | | | | | | | |
snake | .20 | | .07 | .06 | .05 | .04 | .05 | .08 | .12
| | | | | | | | |
_Microtus_ | | | .04 | .02 | .08 | .13 | .09 | .12 | .25
| | | | | | | | |
_Peromyscus_ | | .09 | | .02 | .05 | .06 | .03 | .05 | .04
| | | | | | | | |
"other mammal" | | | | .01 | .04 | .10 | .03 | .03 |
| | | | | | | | |
bird | | | | | | | .01 | .01 |
+-----+-----+-----+-----+-----+-----+-----+-----+----
Total prey items| | | | | | | | |
for size group| 5 | 23 | 28 | 101 | 120 | 121 | 127 | 76 | 24
--------------------+-----+-----+-----+-----+-----+-----+-----+-----+----
The wide disparity in size between young and adult racers also results
in utilization of different food sources to some extent. In some kinds
of snakes adults and young draw their food from entirely different
sources, but in the racer there is broad overlap, as shown in Table 6.
The samples from the largest and smallest size groups of racers are
relatively small. Two important kinds of prey--voles and grasshoppers
of the genus _Melanoplus_--were not found at all in the smallest size
groups of snakes and comprised increasing percentages in the food of
the larger size groups. A large adult vole is too large to be
swallowed except by an unusually large racer, and a young vole old
enough to leave its nest is far too large for a hatchling racer.
Grasshoppers of the genus _Melanoplus_ are relatively large and
heavily armored, and so are relatively immune to attacks from the
smaller snakes. Small soft-bodied orthopterans including _Gryllus_,
_Ceuthophilus_ and _Orchelimum_, and also lizards and snakes, are best
represented in the food of the smaller racers. Other types of prey
showed no definite correlation with size of the racer taking them.
Reproduction
_Sexual Behavior_
Many observers have published accounts of the courtship and/or mating
of the racer, but all of these are, to some degree, incomplete.
Because of the widely different circumstances, and the different
viewpoints of the observers involved, the several accounts give much
different impressions of sexual behavior in this species. Either
singly or combined, the published accounts do not provide an adequate
description of the process.
My own observations, made both under natural conditions and in large
outdoor enclosures, are likewise somewhat incomplete, but indicate
that the whole sequence of courtship and mating is divisible into the
following well-defined stages: 1) the finding of a receptive female by
the male; 2) the persistent following of the female by the male, who
courts her by lying extended along her body and performing writhing
movements, with periodic interruptions during which he momentarily
leaves the female and courses rapidly through the grass around her; 3)
the acceptance of the male by the female, signalled by the raising of
her tail and the almost instantaneous intromission; 4) the dragging of
the passive male by the female while he is firmly attached to her
during the period of coitus; 5) separation of the pair and involution
of the male's hemipenis.
Even in the breeding season, racers that were confined in enclosures
usually were either indifferent to each other or responded with
reactions of fear or hostility. In moving they tended to follow the
edges, and often two moving in opposite directions would approach each
other; when this occurred, one snake might strike at the other with a
short jab that seemed to be mostly bluff, and then would dart away.
The males, being smaller, were usually the more wary.
Sexual behavior was noticed on only a few occasions. Several large
adult males were less wary than others and usually manifested
curiosity or interest toward other racers. My most complete
observations of sexual behavior were made on May 18, 1962, when a
newly caught adult male was added to an enclosure of 100-foot
circumference already containing several racers, two of which were
large adult females. Within half an hour the male was found courting
one of the females. She was lying in a loose coil, with the male
extended along her. At my approach the female darted away in alarm for
approximately three feet, and the male moved with her, so swiftly and
adroitly that he maintained contact and was in approximately his
original position with respect to the female when she stopped.
Spasmodic rippling movements passed down the body of the male as he
lay in contact with the female. These movements lasted several
seconds, increasing in intensity, alternating with longer periods of
little or no movement. As each period of vigorous writhing reached its
climax, the male's head jerked forward and backward several times in
seeming excitement. The female's behavior was mostly passive. She
seemed to be receptive, but from time to time, without any noticeable
warning, she darted away for several feet as she had when the pair was
first discovered. Each time the male darted forward with her,
maintaining contact while she moved. These swift movements of the
female seemed to be spontaneous, at least in most instances there was
no evident cause for alarm. The female's movements seemed to stimulate
the male's interest rather than to discourage him. In most instances
the female moved only four to five feet, then stopped abruptly or
turned back. She would stop in a loose resting coil, in thick grass,
with the male lying over her. Often she coiled in such a way that the
posterior end of her body was beneath her forebody, but this did not
seem to deter the male from moving the posterior end of his body into
position beside hers. After a sudden change in the female's position,
the rear of the male's body would perform groping movements along that
of the female until his cloacal region was approximately opposite
hers. The male sometimes had his chin pressed against the female's
back, especially when he was moving forward along her, but more often
his head was raised, and frequently was as much as 18 inches from the
female's head.
At intervals averaging approximately ten minutes, during a little more
than an hour of observation, the male would suddenly dart away from
the female, and with unusually rapid and animated movements, he would
move around her in an irregular and devious course, sometimes as far
as five feet away, but usually within 18 inches. Usually on each such
expedition several or many circuits were made; then the male would
return to the female and would glide rapidly along her until he
attained the mating position. A period of especially vigorous courting
movements would follow.
At 12:55 p. m. it was necessary for me to discontinue observations,
and I left the female confined in a cloth bag. Returning at 1:20 p. m.
I found that the male was not displaying interest in the female
confined in the bag, nor in the other female loose in the enclosure.
The first female was released from the bag, and was out of sight for
approximately four minutes. When relocated she was again attended by
the male, who was carrying on courtship even more vigorously than he
had before. At 1:35 p. m. the male achieved intromission. Although the
pair was under observation at the time intromission occurred, the
actual eversion of the hemipenis was not seen because the snakes were
partly concealed by dense vegetation. There was a sudden flurry of
movement, the male's head waving and his body thrashing. In an instant
these violent movements subsided, and after a few seconds the female
began to crawl forward slowly. The male had relaxed, and relinquished
his contact with the female anteriorly. As she moved away he was
dragged after her tail-first. He made slight backward wriggling
movements that perhaps aided in maintaining sexual contact. The
female's restlessness increased, and in eight minutes she dragged the
male in a circuitous course a distance estimated to be between 20 and
30 feet. At 1:40 p. m. the pair was ten feet from the point where
copulation had begun. The female showed increasing inclination to
climb, raising her head and forebody against the trunks of saplings,
and finally reaching up one to a branch 20 inches above the ground,
and climbing first along the branch and then farther up the main
trunk. As she progressed the male was lifted from the ground,
dangling limply suspended by his hemipenis and its base had become
exposed. At 1:43 p. m. separation occurred and the male dropped into
the grass. Semen dripped from the cloacae of both snakes. That from
the female was tinged with blood. The individuals involved in this
observation were kept in the enclosure subsequently but no further
sexual behavior was noted.
Contrary to the popular belief that these racers have permanent mates,
all available evidence indicates that they are promiscuous, and two or
more males may simultaneously court the same female in the brief
spring breeding season. On May 24, 1960, while I was walking in a
hilltop field of brome grass, a sudden movement attracted my attention
to three racers lying alongside each other. Only the posterior parts
of their bodies and their tails were visible. Two were males and were
performing the characteristic slow writhing movements against the body
of the female from either side. Although the heads were not in view,
the snakes may have been able to see me through the screening
vegetation; after I had watched for approximately 20 seconds, all
three suddenly took alarm, for no apparent cause, and scattered.
Further evidence of promiscuity is provided by the account of Ellicott
(1880:207) who wrote regarding the eastern subspecies: "I noticed a
ball of black snakes (_Bascanion constrictor_ L) rolling slowly down a
steep and stony hillside ... about two miles above Union Factory,
Baltimore County, Md. ... kept together by procreative impulses." It
was stated that this observation was made in early spring. "Snake
balls" have often been observed, and described in the literature;
usually the snakes involved were garter snakes (_Thamnophis_) or water
snakes (_Natrix_). Seemingly, typical aggregations consist of a single
adult female and several or many males attempting to mate with her.
There is a distinct possibility that the snakes involved in Ellicott's
observations were misidentified.
Sexual behavior of the racer is in most respects remarkably similar to
that of the common garter snake, _Thamnophis sirtalis_, well known
through the work of Blanchard and Blanchard (1942). In studying sexual
behavior of racers, several observers have failed to differentiate
between the different stages of the mating process, and have assumed
that copulation was occurring when actually only the precopulatory
behavior was observed. In an early description of courtship in this
racer in Kansas, Brons (1882:365) stated that the female "at times,
seems to toy with the male, indisposed to yield to his importunities,
though pressed with ardor. To avoid his suit, at times, she will dart
through grass, among stones, or enter a crevice. Should he be able to
reach his mate while within a hole, he is not slow in bringing her to
the surface, again to be repulsed. Upon an unbroken ground the sexual
union is less prolonged. Here she is unable to free herself from his
quick and effectively directed moves. In case she attempts to quit
him, a coil is thrown about her body, and his head laid flat upon her
neck, and replaced as promptly as dislodged, evidently in the endeavor
to propitiate her."
Another account probably based on courtship rather than copulation is
that of Wright and Wright (1957:135), who described the behavior of a
pair of _C. c. priapus_ on Billy Island, Okefinokee Swamp in southern
Georgia, on May 8, 1921, as follows: "They were stretched out, more or
less coiled ... the rear parts of the bodies from the vent were
entwined. The female, or smaller one seemed to have its tail around
that of the male. There were contortions or quiverings from time to
time.... May 8, 1921: Jackson Lee saw black snakes entwined, the male
seizing the female by the top of the neck."
Blanchard and Blanchard (_op. cit._) have described the dragging of
the male by the female during coitus in the garter snake, and the
temporarily inseparable bond formed between members of a pair by the
recurved spines of the engorged hemipenis, but it has not been
generally recognized that the process is much the same in other
colubrines. Cottam (1937:229) described and photographed mating in a
pair of _C. c. mormon_ in Utah. The copulating racers were shown in a
loose coil lying alongside each other with tails intertwined. However,
when disturbed by the observers, these racers made frantic efforts to
escape, crawling in a spiral course, while remaining attached and
intertwined, "with no evident attempt to separate" during
approximately a quarter hour of observation.
The racer is notorious for its aggressive behavior and occasional
alleged attacks on humans in the breeding season. The tendency has
doubtless been much exaggerated, especially in the verbal second- or
third-hand accounts based on the alleged observations of
eye-witnesses. Nevertheless, the supposition that large adults will
sometimes pursue or attack humans when disturbed is well
substantiated. In most of the instances known to me, it is the large
eastern subspecies, _C. c. constrictor_, involved in these incidents,
and seemingly the smaller racers of the Middle West, far West and
South are less inclined to behave aggressively. In May 1958 two pairs
of large racers were confined in a semicircular wire enclosure thirty
feet across and open on top, and with natural vegetation, at the
Reservation headquarters. Often in approaching the cage I saw two or
more racers in close association, but because of sheltering
vegetation, and the snakes' timidity observation was difficult. On May
19 a pair were lying partly extended in loose coils, but immediately
the female took alarm and darted away, breaking loose from the male;
his hemipenis was exposed, and underwent involution and retraction in
approximately 30 seconds. Unlike the female, the male on this occasion
did not attempt to escape, but turned to face me with a show of
aggressiveness. Probably copulation was in its final stages when the
disturbance occurred.
Circling of the female racer by the male from time to time in the
course of courtship has not been recognized by previous observers as a
part of the mating pattern, but Pope (1944:171) described somewhat
analogous behavior, probably modified by unnatural conditions of
captivity and the crowding of many racers in one cage. Pope, citing
earlier observations by Noble, wrote: "When sexually excited, the male
blacksnakes dash wildly about before paying court to individual
females. In captivity these dashes excite all specimens confined
together. A male, after picking out a mate, moves his chin lightly
along her back, while undulations run forward along his sides and he
extends his tongue now and then. Later he throws the part of his body
near his vent over the corresponding part of the female, the two tails
sometimes becoming loosely intertwined."
Recorded dates of mating for the species are all in spring, but
indicate a span of many weeks for the breeding season, and this spread
results in part from geographical differences. Published records are
as follows:
Subspecies _constrictor_
May 12, 1930, in Ohio (Conant, 1938:55)
Subspecies _priapus_
May 8, 1921, in Georgia (Wright and Wright, 1957:135)
May 9, 1921, in Georgia (Wright and Wright, 1957:135)
Subspecies _flaviventris_
May 3, 1931 (two pairs) in Missouri (Boyer and Heinze, 1934:195)
April 18, 1936, in Missouri (Anderson, 1942:210)
May 12, 1928, in Kansas (Gloyd, 1928:123)
Subspecies _mormon_
June 10, 1927, in Utah (Cottam, 1937:229)
July 7, 1938, in California (Cunningham, 1959:17)
In the course of my live-trapping, I occasionally found more than one
racer in a trap. As might be expected from the low yield per trap,
such double or multiple captures were relatively rare. Chance, and
unusually strategic placement of certain traps were doubtless
contributing factors. May and October, being the most productive
months for trapping, yielded a high proportion of these combined
captures. Some involved an adult and an immature snake, or two adults
of the same sex. Eliminating all these, there remain 44 heterosexual
captures of adults. These latter captures are significantly
concentrated in their seasonal distribution and indicate a spring
breeding season; 34 were in May, six were in June and four were in
October. Eight of the May records and one June record each involved a
trio of snakes--two males and a female in every instance. Distribution
of the spring records, grouped in five-day intervals, was as follows:
May 11 to May 15: 14 June 5 to June 9: 0
May 16 to May 20: 5 June 10 to June 14: 2
May 21 to May 25: 8 June 15 to June 19: 2
May 26 to May 30: 13 June 20 to June 24: 0
May 31 to June 4: 1 June 25 to June 30: 1
Approximately 87 per cent of the records fell in the twenty-day
interval, May 11 to 30, which is regarded as the main breeding season.
Presumably males continue to be at the peak of breeding condition and
continue to search for females after the latter have become
unreceptive, partly explaining the scattering of records through most
of June.
Several of the females found in traps with males in May had abundant
active sperm in their cloacae and oviducts and probably had been
inseminated within a few hours of the time they were checked. Others
lacked sperm, but the cramped quarters inside the traps may have
effectively prevented the consummation of courtship, especially when
two males were confined with the same female. None of the females
trapped with males in October was found to be inseminated, and it
seems doubtful whether copulation ever occurs at that time of year,
although males have motile sperm and seem to be in breeding condition
then.
_Cycle of the Male_
Cloacal smears indicate that males mature sexually and first produce
sperm in August and September when they are a little more than a year
old. Insofar as could be determined, there was no sexual activity at
this time of year, and actual breeding of the adolescent racers was
postponed until the following May. By this time at an average age of
20 months, the snakes had made further growth.
[Illustration: Fig. 16. Catches, in semi-monthly periods, of racers in
their summer habitats, at Harvey County Park (upper) and at
Reservation and Rockefeller Tract (lower). Intensive activity in
spring (the breeding season), tapering off rapidly as the season
advances, is well shown by the larger sample, but in the years of
trapping at Harvey County Park operations usually were not fully
underway until the latter part of May.]
Mr. Dwight R. Platt studied the changes in the male reproductive
organs during the annual cycle at Harvey County. In racers recently
emerged from hibernation he found the seminiferous tubules filled with
Sertoli syncytium, but containing few germ cells. Spermatogonia
proliferate in May and June. During the first half of July primary
spermatocytes are the dominant cells in the seminiferous tubules. By
early August spermatids are dominant and the first free spermatozoa
are present. In late October spermiogenesis is essentially complete
and the tubules are relatively empty before the snakes hibernate.
During the season of activity the seminiferous tubules increase to
approximately double their minimum diameter, reaching the maximum in
August. Cyclic changes in size and secretory activity of the ductus
deferens, ductus epididymis, and sexual segment of the renal tubules
occur, with maximum size and secretory activity coinciding with the
time of movement and storage of the spermatozoa. The latter are stored
in both ductus deferens and ductus epididymis. Despite the short
breeding season, a male racer has active sperm at all seasons.
_Eggs_
In accounts of the racer in the humid southeastern United States,
Brimley (1903:261), Wright and Bishop (1915:160) and Tinkle (1959:195)
mentioned the ease with which the eggs might be found and the
superficial situations in which they were sometimes deposited. Both
Wright and Bishop, and Tinkle made field studies in swamps, where
presumably the subsoil was saturated with moisture and too wet for the
eggs. Tinkle mentioned finding one clutch beneath a discarded
newspaper and another beneath a small, thin board. Surface (1906:167)
stated that in Pennsylvania the eggs were to be found in loose soil,
in sawdust piles, or in decaying wood of hollow logs or trees. Clark
(1949:249) stated that in northern Louisiana the eggs are laid in
soft, moist soil such as may be found beside decaying logs. Minton
(1944:457) found two clutches under flat stones on hillsides in
Indiana. In the more arid climates of the far western states the
species' habits are much different in this regard. Through many years
of familiarity with _C. c. mormon_, I have never seen its eggs.
Presumably nests in this part of the range are deep underground, most
often in old burrows of the pocket gopher (_Thomomys_), which are so
abundant that in many areas the soil is riddled with them. Burrows of
the ground squirrels (_Spermophilus_ sp.) and other small digging
mammals also provide potential insulated nest sites with the favorably
moderate temperatures and high humidities that the eggs of snakes
require.
On the morning of July 10, 1962, I was directed to the sites of two
clutches recently plowed up, 1-1/2 miles north of the Reservation (Pl.
21, Fig. 2). The eggs were in a fallow field having a stand of
sunflowers three to five feet high. The plow blades turned the soil at
a depth of approximately seven inches. In each instance only a few
eggs were visible. They were well scattered in the loose soil turned
up by the plow; 21 were found in one clutch and 10 in the other. All
the eggs were intact except two that had minute punctures from which
liquid oozed. Seemingly the eggs _in situ_ had been well above the
level of the blade--at depths of four to five inches. No nest
cavities were discernible where the eggs were found, but elsewhere in
the field tunnels of moles (_Scalopus aquaticus_) and prairie voles
(_Microtus ochrogaster_) were exposed by the plow. Presumably the eggs
had been in such tunnels, which had disappeared as the loose soil
crumbled. Another clutch was discovered in an adjoining field on July
16. The nine eggs were at depths ranging from 6-1/2 to nine inches,
and only the two topmost eggs had been turned up by the plow. All
three clutches were within a few feet of the edges of the fields.
On the Reservation and nearby areas I have seen remains of an
estimated 20 clutches that have been destroyed by predators. The
remains in every instance consisted of an excavation, and the strewn
torn and empty eggshells. Nests were at depths of four to eight inches
in old tunnels, which most often seemed to be those of moles but also
included some of the prairie vole, and perhaps some of the pine vole
(_Microtus pinetorum_). All these nests were in open sunny places in
prairie or pasture habitat.
Table 7. Numbers and Sizes of Eggs in Clutches of the Blue Racer From
Eastern Kansas
========+===============+=================+==============+==============
Number | | | | Snout-vent
of | Lengths | Widths | Weights | length of
Eggs | (mm.) | (mm.) | (grams) | female (mm.)
--------+---------------+-----------------+--------------+--------------
17 | 26.5(29-24) | 17.0(19.0-16.5) | 5.5(6.0-4.4) | 892
8 | 33.3(39-31) | 16.3(17.5-14.0) | 6.0(6.7-5.6) | 899
12 | 29.1(32-25.5) | 17.1(18.5-16.0) | 4.9(5.2-4.4) | 773
14 | 26.9(30-24) | 19.2(20-18) | 5.2(6.2-4.4) | 772
10 | 31.7(33-29) | 16.5(18-15) | 6.0(6.5-5.6) | 807
11 | 29.7(33-27) | 16.7(18-15) | 5.4(5.8-5.0) | 858
21 | 28.9(32-27) | 18.4(19.5-18) | 5.9(6.3-5.6) | 1038
13 | 30.7(34-28) | 19.3(20-18) | 6.8(7.5-6.1) | 907
18 | 29.0(30-26) | 17.9(19-16) | 4.9(5.5-4.3) | 911
12 | 30.3(34-28) | 17.8(19-15) | 5.2(6.1-3.8) | 843
14 | 30.9(36-29) | 19.4(21-18) | 6.8(7.6-6.2) | 846
--------+---------------+-----------------+--------------+--------------
Many observers have described the eggs of the racer, which are white,
elliptical, somewhat elongate, with tough, leathery, somewhat
flexible, shells, and a granular surface. Like other snake eggs, those
of the racer gradually absorb moisture during incubation. They become
more turgid and increase in weight and dimensions, especially in
breadth, and by the time of hatching are nearly twice their size at
laying. Between different clutches and even within the same clutch
there is notable variation in the size of the newly laid eggs. Munro
(1948:199) noted that in a small adult racer kept by him, the eggs
laid were larger but less numerous than those produced by a large
adult. Munro noted also that shape of eggs in the two clutches
differed; the smaller snake produced more elongate eggs of smaller
diameter. The idea that eggs laid by the smaller females are more
slender and elongate is not supported by my own data. For 11 clutches
of eggs examined soon after laying, dimensions, weights, and the
lengths of the females are shown in Table 7.
In a clutch of eggs beginning to hatch on September 3, 1958,
dimensions and weights were as follows: length 31.8 (36-30), diameter
22.0 (24-21), weight 9.7 (10.3-9.3).
Gravid females that were kept in captivity in anticipation of their
laying usually produced their clutches within a few days. The laying
dates of such individuals are shown in the following list. Those with
asterisks were from the Harvey County study area, others were from the
Reservation and Rockefeller Tract.
June 19, 1961 July 1, 1961 July 12, 1961
June 21, 1959 July 4-5, 1962* July 15, 1961*
June 23, 1961* July 6, 1955 July 18, 1961*
June 26, 1959 July 7, 1959* July 20, 1961
June 29-30, 1962* July 7, 1959* August 8, 1960*
A further indication of the period when laying occurs was provided by
the appearance of females gravid and progressively more swollen with
eggs, then their abrupt disappearance and replacement by thin and
wrinkled individuals that obviously were recently parturient. The
following records show the course of these events on the Reservation
in the years when summer trapping was done with sufficient
consistency. These dates provide a rough approximation of the time
when laying occurs locally. They indicate a laying season concentrated
in a period of approximately three weeks in this locality. Records
from published literature also indicate that laying occurs in late
June and early July at the latitude of Kansas, but somewhat earlier in
the southern United States.
Table 8. Dates When Parturient and Gravid Racers were Captured on
Reservation and Rockefeller Tract in Several Years, Indicating Time
of Oviposition
========================+=========+=========+=========+=========+========
Year | 1958 | 1959 | 1960 | 1961 | 1962
------------------------+---------+---------+---------+---------+--------
First parturient female | June 18 | June 17 | June 22 | June 20 | June 13
Last gravid female | July 8 | July 11 | July 5 | July 12 | July 16
------------------------+---------+---------+---------+---------+--------
Many authors have made statements regarding the size of the clutch in
the racer, on the basis of those found in the field, those laid after
capture, or those dissected from gravid females. Some of the
statements were based upon small but unspecified samples, and are far
from the mark. From records accumulated in the course of my own field
work, and a summarization of those in published accounts a substantial
sample is available showing the usual size of clutch in the area of my
study, and the trends of geographic variation in some parts of the
range.
_C. constrictor_ (all combined)
151 clutches averaged 10.61 (2 to 31) eggs.
_C. c. constrictor_ 14 clutches averaged 16.80 (7 to 31) eggs.
_C. c. priapus_ 11 clutches averaged 12.60 (7 to 21) eggs.
_C. c. mormon_ 43 clutches averaged 5.79 (2 to 13) eggs.
_C. c. flaviventris_ 82 clutches averaged 11.78 (5 to 26) eggs.
_C. c. stejnegerianus_, one clutch contained 10 eggs.
In the foregoing list the sample of _C. c. flaviventris_ may be
divided as follows:
Reservation and vicinity: 36 clutches averaged 11.65 (6 to 21) eggs.
Harvey County study area: 21 clutches averaged 12.0 (5 to 18) eggs.
Museum specimens from Kansas: five clutches averaged 9.2 (6 to 14)
eggs.
Published records (Kansas, Indiana, Iowa, Louisiana, Missouri,
Oklahoma, Texas): 20 clutches averaged 12.5 (5 to 22) eggs.
Table 9. Published Records Indicating Dates of Laying in Different
Populations of Coluber constrictor
===============+==================+============+=========================
Date | | |
of Laying | Subspecies | Area | Authority
---------------+------------------+------------+-------------------------
June 9, 1952 | _flaviventris_ | SE Texas | Guidry (1953:50)
July 1-2, 1920 | _flaviventris_ | Texas | Ortenburger (1928:183)
June 1, 1920 | _flaviventris_ | Texas | Ortenburger (1928:183)
June 9, 1926 | _flaviventris_ | Oklahoma | Force (1930:31)
June 24, 1926 | _flaviventris_ | Oklahoma | Force (1930:31)
July 19, 1928 | _flaviventris_ | Oklahoma | Force (1930:31)
July 16 | _flaviventris_ | Oklahoma | Carpenter (1958:114)
July 4-5, 1948 | _flaviventris_ | Kansas | Munro (1948:199)
July 4, 1948 | _flaviventris_ | Kansas | Munro (1948:199)
June 26, 1930 | _flaviventris_ | Ohio | Conant (1938:55)
July 3, 1961 | _mormon_ | NW Oregon | Van de Velde, Martan
| | | and Risley (1962:212)
June 7, 1957 | _priapus_ | S Illinois | Rossman (1960:219)
June 19, 1912 | _priapus_ | S Georgia | Wright and Bishop
| | | (1915:160)
July 10, 1940 | _priapus_ | S Illinois | Cagle (1942:187)
July 6 | _constrictor_ | New York | Ditmars (1907:284)
June 27-July | _constrictor_ | Virginia | Werler and McCallion
5, 1951 | | | (1951:251)
June 5, 1947 | _stejnegerianus_ | S Texas | Auffenberg (1949:54)
---------------+------------------+------------+-------------------------
Published records of clutches laid by racers, from which figures used
in the foregoing account were obtained, include the following:
_C. c. constrictor_: 22 (Barbour, 1950:104); 21, 13 (Brimley,
1903:261); 25 (Conant, 1938:55); 8 (Ditmars, 1907:284); 7,
12, 14, 16, 19, 20, 31 (McCauley, 1945:76); 14 (Wright and
Wright, 1957:136).
_C. c. flaviventris_: 7 (Anderson, 1942:210); 22 (Brumwell,
1951:205); 11 (Carpenter, 1958:114); 8, 9, 9 (Force,
1930:31); 10 (Guidry, 1953:50); 18 (Liner, 1949:230); 5, 8,
17 (Marr, 1944:484); 5, 14 (Munro, 1948:199); 13, 19
(Ortenburger, 1928:183); 6, 15 (Tinkle, 1959:195); 15, 19
(Wright and Wright, 1957:141).
_C. c. priapus_: 20, 21 (Cagle, 1942:187); 7 (Conant,
1938:55); 19 (Rossman, 1960:219); 5, 9, 11, 14 (Wright and
Bishop, 1915:160); 16 (Wright and Wright, 1957:147).
_C. c. mormon_: 13, 9, 8, 5, 5, 5, 4, 4 (Cunningham,
1959:17); 5, 6 (Stebbins, 1954:374); 6 (Van de Velde,
Martan and Risley, 1962:212); 3, 6 (Wright and Wright,
1957:144):
_C. c. stejnegerianus_: 10 (Auffenberg, 1949:54).
In general, the number of eggs in the clutch is proportional to the
size of the female producing them. The larger and bulkier females
produce more eggs. Geographic trends in number of eggs produced are
perhaps controlled by differences in size between different
populations; thus, the large eastern _constrictor_ produces nearly
three times as many eggs per clutch as does the small western
_mormon_, whereas the centrally located _flaviventris_ is somewhat
intermediate in size and in numbers of eggs produced.
In most reptiles growth in length and bulk continues after attainment
of sexual maturity. For many kinds including _Eumeces fasciatus_,
_Crotaphytus collaris_, _Cnemidophorus sexlineatus_, _Agkistrodon
contortrix_ (Fitch, 1954:60; 1956:236; 1958:36; 1960:174), and
_Sceloporus olivaceus_ (Blair, 1960:94), it has been shown that the
larger and older females in a population produce more offspring than
do the smaller and younger individuals. This situation applies in the
racer, as shown by the clutches of 52 females correlated with their
sizes and presumed ages (Fig. 17, Table 10). The two-year-olds
contribute a relatively small quota to the annual brood, partly
because their clutches are small, but more especially because many of
them fail to attain sexual maturity in time to breed. Many of the
female racers that are more than two years old also fail to produce an
annual clutch of eggs. The 24-day period May 28 to June 20 inclusive
is judged to comprise the period when eggs have generally enlarged
sufficiently to be detected in gravid females, but still have not been
laid in most instances. In this period, in 1960, 1961 and 1962, ratios
of gravid females to those not detectably gravid in several supposed
age groups arbitrarily established on the basis of size, were as
follows:
Two-year-olds 2 gravid, 13 apparently not gravid
Three-year-olds 5 gravid, 4 apparently not gravid
Four-year-olds 3 gravid, 2 apparently not gravid
Five-year-olds 4 gravid, 3 apparently not gravid
Six-year-olds (or older) 8 gravid, 2 apparently not gravid
[Illustration: Fig. 17. Graph showing number of eggs per clutch, and
correlation with supposed age (as deduced from length of body) in
female blue racers from the Reservation, Rockefeller Tract, and Harvey
County Park.]
From the appearance of these snakes it is reasonably certain that none
had already laid eggs when it was recorded, but there is some
possibility that a few individuals not noticeably gravid at the times
they were examined, produced eggs subsequently. However, these meager
data do seem to indicate that most of the two-year-old females and a
minority of older individuals fail to produce clutches in the annual
breeding season.
Table 10. Fecundity of Female Racers in Various Age-size Classes,
All From the Reservation and Rockefeller Tract
========================+===========+=====================+==============
Most Probable Age | Number of | Snout-vent length | Number
in Years of Females | females | of females; average | of eggs in
(as indicated by size) | in sample | and extremes | clutch
------------------------+-----------+---------------------+--------------
2 | 10 | 688 (589-748) | 9.2 (6-12)
3 | 19 | 789 (756-840) | 9.9 (5-14)
4 | 7 | 856 (850-861) | 10.8 (8-12)
5 | 6 | 907 (892-933) | 13.0 (8-17)
6 or more | 10 | 1005 (955-1088) | 15.7 (11-19)
------------------------+-----------+---------------------+--------------
Under unfavorable conditions eggs can be resorbed, but probably this
can occur only if initiated before ovulation. A racer in which six
small eggs were palped on June 28, 1960, was kept until July 23 but
did not oviposit. It no longer appeared gravid and the ova could not
be detected by palpation. Another female had 13 eggs on June 21, 1960,
but by July 23 when the snake was released the eggs had not been laid
and no longer could be detected. Both snakes refused to feed
throughout their confinement.
Like other reptilian eggs, those of the racer are dependent upon the
warmth of their surroundings for incubation. They are tolerant of a
wide range of environmental temperatures, but the higher the
temperature the more rapidly incubation proceeds. Under natural
conditions there may be much difference in hatching time in two
clutches laid at the same time and in the same locality. Site of the
nest--deep and well insulated, or shallow; in a well shaded situation
or one exposed to maximum amounts of sunshine--would largely control
rates of development. Clark (1949:249) writing of the subspecies
_anthicus_ in north-central Louisiana, stated: "eggs are laid about
the first of June.... young begin to make their appearance at about
... July 1." Even for the southern states these dates of laying and
hatching seem somewhat too early to reconcile with the records
published by other observers, and are in need of verification,
especially since they seem to be based upon vaguely remembered
observations rather than upon written records. At the other extreme
Surface (1906:167) wrote of _constrictor_ in Pennsylvania that
hatching may occur as late as October, and that there is evidence some
young may even remain in the egg over winter before hatching occurs.
Several incubation periods are on record for clutches laid and hatched
in captivity, as follows:
_C. c. mormon_, Oregon, 47 and 51 days (laid July 3, 1961,
hatched August 19 and 23; Van de Velde, Martan and Risley,
1962:212).
_C. c. stejnegerianus_, Texas, 73 days (laid June 5, 1947,
hatched August 17, Auffenberg, 1949:54).
_C. c. priapus_, S. Illinois, 58 and 59 days (laid July 10,
1940, hatched September 6 and 7, Cagle, 1942:187).
_C. c. flaviventris_, Kansas, 50 days (laid July 4 and 5,
hatched August 23 and 24; Munro, 1950:124).
_C. c. flaviventris_, Texas, 43 days (laid June 9, 1952,
hatched July 22; Guidry, 1953:50).
No incubation periods for eggs in natural nests have been recorded. In
the course of my study, eggs obtained from 12 captive females were
hatched in confinement, with an average incubation period of 51 days
(43 to 63) as follows:
Laid July 6, 1955, hatched August 20.
Laid July 3, 1958, hatched September 3 and 4.
Laid June 21, 1959, hatched August 17.
Laid June 26, 1959, hatched August 17.
Laid July 7, 1959, hatched August 23 to 25.*
Laid June 23, 1960, hatched August 20.*
Laid June 30, 1961, hatched August 30.
Laid July 15, 1961, hatched September 1 and 2.*
Laid July 18, 1961, hatched September 2 and 3.*
Laid July 4 and 5, 1962, hatched August 15 and 16.*
Laid June 29 and 30, 1962, hatched August 14 and 15.*
Laid July 6, 1962, hatched August 16 to 20.*
In the foregoing list those entries marked with asterisks were
obtained from the Harvey County study area; all others were from the
Reservation and Rockefeller Tract.
_Hatching_
Detailed observations on hatching were made on a clutch of eggs laid
on June 29 and 30, 1962, by a female caught in Harvey County. The
first egg in the clutch had already been laid in the trap when the
female was found at 11:30 a. m., June 29. Two of the eggs were
abnormal, with thin transparent shells, and were found to lack embryos
when they were opened on July 7. Later, two other eggs were attacked
by mold and the embryos died early in development. The clutch was kept
in a can of slightly damp soil. At 2:30 p. m. on August 13, when the
clutch was examined, egg no. 6 was found to have hatched. The young
snake had made a 21-millimeter slit in the shell. At 12:50 a. m. on
August 14, it was discovered that eggs 1, 4, 5 and 7 each had been
slit. No. 4 had two parallel slits separated by a two-millimeter strip
of shell, and the young racer could be seen inside. At 1:05 a. m.
this young snake had changed position and was lying upside down in the
egg, his snout protruding slightly through one of the slits. At 1:45
a. m. he was again right side up, still in the shell. At this time
each of the slit eggs showed the protruding snout of a young snake.
Occasionally the viscous liquid egg white would be blown into a large
bubble on the surface of the shell as the young snake exhaled. A third
slit, parallel to the others, had appeared in egg no. 4. A hatchling
emerged from egg no. 1 between 2:20 and 3:20 a. m., and another from
no. 7 between 7:00 and 9:00 a. m. The hatchling struck vigorously many
times, and vibrated his tail when he was disturbed. Egg no. 3 was
first slit between 7:00 and 9:00 a. m., and three more slits appeared
in it between 9:15 and 10:15 a. m. At 12:45 p. m. a hatchling was
found in the act of emerging from egg no. 4, and approximately the
anterior one-fourth of its body protruded. Disturbed by the movements
of the observer, the little snake drew back into its shell. This
hatchling began to emerge again at 12:50 and his hatching was
completed at 1:00 p. m. Between 5:40 and 6:20 p. m. a hatchling
emerged from egg no. 3 (for several hours this hatchling had been
lying on its back inside the egg, with only its snout protruding); two
slits appeared in egg no. 2 and three slits appeared in egg no. 8. At
6:50 p. m. the hatchling in the latter thrust his snout through the
slit in this eggshell. This hatchling was lying on its back at first
but by 10:50 it had shifted to a normal position. It emerged from the
shell between 2:35 and 2:50 a. m. Egg no. 2 was the last to hatch. At
7:05 p. m. the hatchling inside made two additional small slits in the
shell, and at 7:30 p. m. thrust its snout through one of them, while
lying on its back. At 1:45 a. m. it was right side up, but at 3:00 a.
m. had reverted to its previous position. At 4:40 a. m. it was again
right side up, and it emerged from the shell at 5:55 p. m.
On August 17, at 11:00 a. m., hatchlings no. 5 and no. 6 had lost
their egg teeth. All others still had their egg teeth then, but by
10:00 p. m. that of no. 8 was missing, and that of no. 4 was loose and
dropped out while the snake was being handled. On August 20 at 9:00 a.
m., hatchling no. 7 had lost its egg tooth; nos. 2 and 3 retained
theirs only in part, and no. 1 had its egg tooth intact. By noon on
August 22 no trace of an egg tooth remained on any of the hatchlings.
In the same group of hatchlings sign of impending molt was first
noticed on the morning of August 17, when no. 6 was noted to have its
eyes clouded and milky in appearance. By evening no. 1 had attained
the same stage and no. 7 was beginning to show it. On the morning of
August 20, shedding had begun in no. 6, while no. 2 and no. 8 had
milky eyes. The eyes had cleared in no. 1 and no. 7, and were still
clear in the remaining hatchlings. On August 22 shedding had been
completed by no. 1 and no. 8, and all others were in the process of
shedding.
Another clutch of 14 eggs from a recently captured female was found
freshly laid in a cage on July 6, 1962. Hatching of 13 occurred August
16 to 20, as shown in Table 11.
Table 11. Times of Hatching in a Clutch of Racer Eggs From Harvey
County Park
========+================================+=============================
| Time at which shell | Time that hatchling
Number | was slit by hatchling | emerged
of Egg +---------+----------------------+---------+-------------------
| Day | Hour | Day | Hour
--------+---------+----------------------+---------+-------------------
1 | Aug. 17 | 10:50 a. m. | Aug. 18 | 3:00 to 6:00 p. m.
2 | Aug. 17 | 12:15 to 12:50 p. m. | Aug. 18 | 3:25 to 4:25 p. m.
3 | Aug. 17 | 1:40 p. m. | Aug. 17 | 10:45 p. m.
4 | Aug. 18 | 3:00 to 6:00 p. m. | Aug. 19 | before 7:00 a. m.
5 | Aug. 16 | 10:45 a. m. | Aug. 17 | 6:30 to 7:55 a. m.
6 | Aug. 17 | 9:00 a. m. | Aug. 18 | 6:30 to 7:30 a. m.
7 | Aug. 17 | 4:15 p. m. | Aug. 20 | 1:00 to 7:00 a. m.
8 | Aug. 17 | 3:40 p. m. | Aug. 18 | 5:00 to 6:00 p. m.
9 | Aug. 17 | 7:30 p. m. | Aug. 18 | 6:30 to 7:30 a. m.
10 | Aug. 16 | 10:48 a. m. | Aug. 17 | 11:05 a. m.
12 | ? | no record | Aug. 18 | 6:00 to 6:30 a. m.
13 | Aug. 17 | 8:00 to 8:20 a. m. | Aug. 17 | 5:30 to 5:50 p. m.
--------+---------+----------------------+---------+-------------------
Growth
Hatching usually occurs in late August or early September, and the
disparity in size between hatchlings and adults is greater than in
some other kinds of snakes. In 76 young from ten clutches of eggs
incubated in the laboratory, averages and extremes for measurements
and weights were as follows: snout-vent length, 214.5 (186 to 244)
millimeters; tail, 59.3 (44 to 73) millimeters; weight, 4.16 (2.4 to
5.8) grams. In each brood the size tended to be fairly uniform, except
that there were usually one or more stunted individuals markedly
smaller than the others. However, there were striking differences in
size between the young of different broods. None of the young captured
was as small as the average hatchling from the clutches incubated in
captivity, but in the 14 years of my study only four young were
captured in August. The hatchlings are relatively secretive and
elusive, and the lush vegetation of late summer provides them with
abundant hiding places. Nevertheless it is remarkable that the
hatchlings are so seldom seem, when their probable abundance is taken
into account.
Probably all of those captured had already made some growth after
hatching. By early November or the last week of October, racers have
almost or quite completed their season of activity, and are at the
hilltop ledges, preparing to hibernate, if they have not already
retired into dormancy. For 25 young of the year captured in this
period at the end of the growing season, measurements and weights were
as follows: snout-to-vent, 327 (273 to 418) millimeters; tail 93 (72
to 114) millimeters; weight, 12.3 (7 to 19) grams. In the ten-week
period between hatching and hibernation these young had already passed
through their period of most rapid growth, having added, on the
average, more than 50 per cent to their original lengths, and almost
tripled in weight. In these young about to enter their first
hibernation, variation in size and weight is much greater than in the
hatchlings; some have fared much better than others, and there are
significant age differences. Within any one year the time of hatching
is spread over several weeks because of differences in the time of
laying, and differences in nest sites, with variation in heat
received, which promotes or delays the rate of incubation. Year to
year differences in the trend of weather increase the dispersion as
the incubation time is shortened in hot, dry summers and lengthened in
those that are relatively cool and moist.
Table 12. Growth of First-year Racers
=====+=================================+=================================
| Original record | Record(s) of recapture
+---------------+--------+--------+---------------+--------+--------
| | Snout- | | | Snout- |
Sex | | vent | | | vent |
| Date | length,| Weight,| Date | length,| Weight,
| | milli- | grams | | milli- | grams
| | meters | | | meters |
-----+---------------+--------+--------+---------------+--------+--------
[M] | Aug. 17, 1959 | 223 | 5.3 | Sept. 12, 1960| 503 | 42
[F] | Oct. 26, 1959 | 278 | 10 | Oct. 26, 1959 | 566 | 55
[F] | Nov. 2, 1959 | 340 | 18 | May 11, 1961 | 582 | 65
[F] | Nov. 10, 1959 | 348 | 13.7 | June 20, 1961 | 733 | 127
[F] | Oct. 19, 1952 | 361 | 15.3 | Oct. 9, 1953 | 620 | 68
[M] | May 9, 1953 | 368 | 17 | May 13, 1954 | 609 | 84
[F] | April 16, 1950| 328 | 142 | Oct. 10, 1950 | 603 | 78.2
[F] | May 17, 1956 | 358 | 15.2 | Oct. 6, 1956 | 575 | 52
[M] | Nov. 1, 1953 | 330 | 11 | May 21, 1955 | 674 | 92
-----+---------------+--------+--------+---------------+--------+--------
Though covering a wide size-range, the young of the year entering
hibernation are still a distinct size group, not yet overlapping that
of the next older group of young. Growth during the first year of life
is best shown by the individuals in Table 12, all of which were marked
either before their first hibernation or soon after emerging from it,
and were recaptured either the following autumn, or in spring soon
after emerging from a second hibernation.
These records indicate that the young racers at the time of their
second hibernation have grown to a snout-vent length of well over 500
millimeters, but less than 700 millimeters, and a weight of more than
40 grams but less than 100 grams. Other racers marked in the first few
weeks of life were recaptured after two or more seasons of growth, and
indicate the sizes that may be expected in young adults from two to
five years old, as shown in Table 13.
Table 13. Growth of Racers Marked at an Age of Less Than One Year and
Recaptured in Their Second, Third or Fourth Years
Column headings:
A: Snout-vent length in mm.
B: Weight in grams
C: Probable age in months
====+=================================+==================================
| Original record | Record(s) of recapture
Sex +---------------+-----+----+------+--------------+-----+-----+-------
| Date | A | B | C | Date | A | B | C
----+---------------+-----+----+------+--------------+-----+-----+-------
[M] | Nov. 12, 1952 | 342 |....| 2-1/2| May 20, 1955 | 702 | 110 | 33
[M] | Nov. 1, 1953 | 330 | 11 | 2 | Aug. 16, 1956| 780 | 162 | 35-1/2
[M] | Nov. 12, 1953 | 293 |....| 2-1/2| May 14, 1956 | 634 | 96 | 32-1/2
| | | | | Oct. 13, 1956| 689 | 110 | 37-1/2
[M] | April 15, 1955| 320 | 13 | 9-1/2| June 8, 1958 | 740 | 118 | 45
[M] | Oct. 2, 1955 | 348 | 18 | 1 | May 22, 1958 | 728 | 120 | 33
| | | | | May 21, 1960 | 795 | 130 | 57
[M] | June 25, 1959 | 378 | 10 | 10 | June 30, 1960| 590 | 60 | 22
| | | | | June 7, 1961 | 705 | 123 | 33
[M] | Nov. 1, 1953 | 330 | 11 | 2 | Aug. 25, 1957| 805 | 183 | 48
----+---------------+-----+----+------+--------------+-----+-----+-------
Unlike young of the year, racers in their second autumn were trapped
in large numbers. By this time all were large enough to be caught in
the traps of quarter-inch wire mesh, and they were the most abundant
size group. Many that were marked at this stage were recaptured after
intervals of months or years, showing the trend of growth. Some of
these snakes in their second autumn already had overtaken the more
retarded third-year individuals. The two age classes cannot be
separated with certainty. Selected records of individuals that were
almost certainly second-year young at the time they were marked are
presented in Table 14.
Table 14. Growth of Young Racers That Were Marked Near the Time of
Their Second Hibernation
Column headings:
A: Snout-vent length in mm.
B: Weight in grams
C: Probable age in months
====+==================================+====================================
| Original record | Record(s) of recapture
Sex +--------------+-----+-----+-------+---------------+-----+------+-------
| Date | A | B | C | Date | A | B | C
----+--------------+-----+-----+-------+---------------+-----+------+-------
[M] | Oct. 6, 1960 | 595 | 80 | 13 | July 23, 1961 | 650 | 70 | 23
[M] | Oct. 13, 1950| 525 | 52.6| 13-1/2| Oct. 2, 1951 | 675 | 105 | 25
[M] | Nov. 2, 1950 | 545 | 55.6| 14 | Oct. 24, 1951 | 670 | 100 | 26
[M] | Sept. 2, 1957| 522 | 57 | 12 | Oct. 14, 1958 | 690 | 103 | 25-1/2
[M] | Oct. 17, 1953| 558 | 47 | 13-1/2| May 10, 1955 | 718 | .... | 32
[M] | Nov. 14, 1956| 587 | 57 | 14-1/2| May 20, 1958 | 728 | 100 | 52-1/2
| | | | | June 17, 1959 | 880 | 219 | 64-1/2
[M] | Sept. 7, 1959| 533 | 45 | 12 | June 6, 1961 | 740 | 112 | 33
[M] | Oct. 17, 1959| 558 | 56 | 13-1/2| July 21, 1960 | 625 | 63 | 22-1/2
| | | | | June 7, 1961 | 670 | 95 | 33
[M] | Oct. 16, 1952| 577 | 62.0| 13-1/2| May 31, 1955 | 809 | 160 | 45
| | | | | May 11, 1956 | 855 | 144.3| 56-1/2
[M] | Oct. 11, 1950| 570 | 65.9| 13-1/2| July 11, 1956 | 820 | 193.6| 82-1/2
[M] | Oct. 14, 1953| 560 | 52 | 13-1/2| June 29, 1958 | 794 | 256 | 70
[M] | Oct. 6, 1950 | 563 | 55.8| 13 | Sept. 28, 1958| 907 | 243 | 109
[M] | Oct. 14, 1953| 523 | 44 | 13-1/2| May 19, 1959 | 818 | 190 | 80-1/2
| | | | | May 17, 1960 | 850 | 211 | 92-1/2
[M] | Oct. 13, 1953| 521 | 50.1| 13-1/2| May 13, 1958 | 814 | 166.4| 44-1/2
| | | | | June 3, 1959 | 826 | 165 | 47
[M] | Nov. 5, 1953 | 512 | 34 | 14 | May 22, 1958 | 847 | 135 | 69
[F] | Aug. 11, 1953| 534 | 39.2| 11-1/2| Sept. 18, 1954| 670 | 143 | 24-1/2
[F] | Oct. 14, 1949| 588 | 55.2| 13-1/2| Oct. 11, 1950 | 713 | 114.0| 25-1/2
[F] | Oct. 6, 1950 | 570 | 60.4| 13 | Oct. 11, 1951 | 783 | 174 | 25-1/2
[F] | Oct. 31, 1953| 582 | 58 | 14 | Oct. 5, 1954 | 860 | 195 | 25
[F] | Oct. 21, 1959| 588 | 63 | 13-1/2| May 7, 1961 | 730 | 120 | 32
[F] | May 14, 1960 | 506 | 34 | 20-1/2| Oct. 26, 1960 | 690 | 90 | 26
[M] | Oct. 22, 1960| 527 | 45 | 13-1/2| Oct. 7, 1961 | 620 | 74 | 25
[M] | May 3, 1960 | 530 | 48 | 20 | May 16, 1961 | 700 | 110 | 32-1/2
[M] | May 27, 1961 | 535 | 40 | 21 | Oct. 25, 1961 | 672 | 98 | 26
----+--------------+-----+-----+-------+---------------+-----+------+-------
From the records in Table 14 and many more like them, average and
extreme sizes for progressively older age groups were estimated. Even
racers that were already of adult size when they were marked were
tentatively identified with one or another age group, and their
records of subsequent growth were used. Most of the records show that
the females grow more rapidly than the males, and are, on the average,
larger at any given age.
Relatively few individual racers were recaptured after periods of
several years. Each of the eight listed in Table 15 is among those
that were captured in four or more different years, and their records
are significant in revealing the trend of growth after sexual maturity
has been attained. These snakes, one to three years old at the time
they were marked, show well the persistent but decreasing growth, and
the fluctuating weight that is characteristic of this and other
species.
[Illustration: Fig. 18. Graph from records of blue racers marked early
in life and recaptured, showing average and extreme snout-vent lengths
for males and females of various ages. Growth is especially rapid in
the first year, but continues, with gradual slowing, throughout life.
In hatchlings, the sexes are of approximately equal size, but females
grow to be markedly larger than males.]
Some of the largest racers recorded had already reached unusually
large size when they were first captured, so there was no opportunity
to determine their ages. Several others, originally captured as small-
or medium-sized adults, subsequently grew to a size approaching the
maximum, and thus provided a basis for estimating the ages of large
individuals. The records of nine such racers are listed in Table 16.
Table 15. Changes in Lengths and Weights in Eight Racers Recaptured
Repeatedly Over Periods of Years
=====================+=============+=============+========+==========
| Snout-vent | Tail length | Weight | Probable
Date of Capture | length in | length in | in | age in
| millimeters | millimeters | grams | months
---------------------+-------------+-------------+--------+----------
_No. 1, male_ | | | |
October 21, 1953 | 676 | 216 | 85 | 25-1/2
October 12, 1954 | 733 | 238 | 128 | 37-1/2
July 31, 1955 | 755 | 243 | 143 | 46
May 20, 1956 | 785 | 250 | 153 | 55-1/2
July 15, 1957 | 788 | 252 | 162 | 69-1/2
June 30, 1958 | 820 | 264 | 200 | 81
May 15, 1959 | 828 | 263 | 195 | 91-1/2
May 14, 1960 | 840 | 265 | 195 | 103-1/2
_No. 2, male_ | | | |
May 9, 1955 | 678 | 212 | 105 | 32
May 26, 1958 | 827 | 248 | 195 | 69
May 3, 1959 | 865 | 262 | 218 | 80
May 14, 1960 | 877 | 264 | 218 | 92-1/2
July 16, 1960 | 890 | 257 | 190 | 94-1/2
_No. 3, male_ | | | |
May 26, 1955 | 565 | 171 | 53 | 21
August 28, 1957 | 798 | 245 | 155 | 48
May 13, 1958 | 814 | 249 | 137 | 56-1/2
May 4, 1959 | 848 | 252 | 180 | 68
June 12, 1961 | 896 | 262 | 198 | 93-1/2
_No. 4, male_ | | | |
May 19, 1956 | 632 | 208 | 78 | 20-1/2
August 2, 1957 | 740 | 238 | 123 | 35
May 20, 1959 | 796 | 246 | 132 | 56-1/2
May 23, 1960 | 813 | 280 | 140 | 68-1/2
_No. 5, male_ | | | |
June 30, 1956 | 594 | 188 | 73 | 22
October 12, 1956 | 658 | 200 | 80 | 27-1/2
July 14, 1957 | 690 | 220 | 102 | 34-1/2
June 23, 1958 | 749 | 226 | 136 | 46
July 24, 1959 | 751 | 239 | 133 | 59
May 27, 1960 | 765 | 235 | 130 | 69
_No. 6, male_ | | | |
October 19, 1956 | 518 | 167 | 43 | 13-1/2
July 19, 1957 | 673 | 218 | 96 | 22-1/2
May 5, 1960 | 780 | 250 | 175 | 56
May 9, 1961 | 840 | 272 | 272 | 68
_No. 7, female_ | | | |
May 12, 1957 | 790 | 238 | 175 | 32-1/2
September 3, 1957 | 810 | 243 | 208 | 36
October 1, 1958 | 883 | 259 | 206 | 49
July 11, 1959 | 915 | 247[A] | 190 | 58-1/2
September 12, 1960 | 930 | 249[A] | 238 | 72-1/2
September 14, 1961 | 1012 | 268[A] | 332 | 84-1/2
_No. 8, female_ | | | |
June 23, 1955 | 601 | 175 | 67 | 22
August 3, 1958 | 920 | 255 | 300[B] | 60
July 23, 1959 | 955 | 281 | 211 | 71
May 18, 1960 | 962 | 262 | 260 | 81
---------------------+-------------+-------------+--------+----------
[A] Incomplete.
[B] With food.
[Illustration: Fig. 19. Graph from records of blue racers marked early
in life and recaptured, showing average and extreme weights in samples
of different ages. Early in life the females outstrip males in growth
and the size differential increases throughout life.]
A few adult racers recaptured, including different individuals of
small, medium, and large size, failed to make any measurable gain in
length over periods of months, or even over several years. Most often
the large individuals were those that failed to grow or made only
slight gains. Some of the snakes that failed to increase in length
suffered dramatic weight losses, perhaps as a result of injury,
disease, or parasitism. However, other individuals that failed to gain
appreciably in length did gain in weight. Doubtless both genetic and
environmental factors were involved. A few racers gave the impression
of being stunted by adversity. All records obtained of growth (or
failure to grow), throughout the period of my study were used in
compiling Table 17.
Table 16. Growth in Several Racers That Were Already Adult When
Originally Captured and That Subsequently Attained Unusually
Large Size
Column headings:
A: Snout-vent length in mm.
B: Weight in grams
C: Probable age in months
====+==================================+====================================
| Original record | Record(s) of recapture
Sex +--------------+-----+-----+-------+--------------+------+-----+--------
| Date | A | B | C | Date | A | B | C
----+--------------+-----+-----+-------+--------------+------+-----+--------
[M] | May 14, 1956 | 815 | 191 | 56-1/2| May 15, 1959 | 905 | 243 | 92-1/2
| | | | | May 16, 1961 | 945 | 287 | 104-1/2
[M] | May 22, 1958 | 825 | 251 | 68-1/2| June 25, 1959| 840 | 205 | 82
| | | | | May 27, 1960 | 880 | 210 | 93
| | | | | Oct. 14, 1961| 900 | 223 | 109-1/2
[M] | May 19, 1959 | 705 | 105 | 32-1/2| May 28, 1960 | 828 | ... | 45
| | | | | July 3, 1961 | 900 | 265 | 58-1/2
[F] | Nov. 6, 1954 | 823 | 190 | 38 | June 30, 1958| 1030 | 350 | 82
[F] | June 6, 1955 | 810 | 190 | 33 | May 21, 1959 | 1087 | 345 | 80-1/2
[F] | Aug. 29, 1957| 885 | 265 | 48 | Aug. 6, 1960 | 1041 | 235 | 83
[F] | May 1, 1958 | 633 | 84 | 20 | May 30, 1961 | 1088 | 320 | 57
[F] | July 20, 1958| 862 | 203 | 46-1/2| June 30, 1960| 1020 | 238 | 70
[F] | Oct. 18, 1956| 845 | 185 | 37-1/2| May 20, 1958 | 905 | 240 | 56-1/2
| | | | | Oct. 22, 1959| 1085 | 375 | 74
----+--------------+-----+-----+-------+--------------+------+-----+--------
Mortality Factors and Adaptations for Survival
_Defense, and Escape_
The behavior patterns that are associated with defense and escape in
snakes are widespread. The common racer is typical of the more
generalized snakes. Almost all elements of the racer's behavior are
found in snakes of other genera and perhaps, of other families. The
racer differs from these only in minor details of its behavior, in the
circumstances under which various behavioral traits are elicited, and
their relative importance. The common racer is one of the swiftest of
North American snakes, and it usually depends upon speed to avoid
enemies. Racers crossing roads may detect approaching automobiles at a
distance, and thereby may be stimulated to accelerate their movements
and so escape onto the shoulders rather than becoming traffic
casualties as many individuals of most other kinds of snakes do under
the same circumstances. The chances of such escape are of course much
better on dirt roads that are relatively narrow and have a rough
surface permitting efficient traction, than on wide smooth, paved
highways. The snakes are somewhat reluctant to venture onto open
expanses of pavement.
Table 17. Sizes of Racers of Different Age Groups in May and October
========+====================================================
| Males
+-------------------------------+--------------------
Age in | Snout-vent length in mm. | Weight in grams
Years +---------+----------+----------+---------+----------
| | Typical | Observed | | Observed
| Average | range | range | Average | range
--------+---------+----------+----------+---------+----------
1+ | 539 | 432-609 | | |
2- | 615 | 500-676 | 560-674 | 68.2 | 51-92
2+ | 668 | 610-700 | 620-710 | 107.4 | 63-134
3- | 706 | 677-730 | 648-755 | 102.1 | 65-129
3+ | 740 | 701-754 | 667-780 | 147.0 | 93-216
4- | 757 | 731-772 | 725-809 | 139 | 95-251
4+ | 785 | 755-793 | 720-850 | 167.4 | 128-225
5- | 805.5 | 773-810 | 743-855 | 152.4 | 110-198
5+ | 810 | 801-831 | 773-858 | 163.9 | 89-211
6- | 827 | 811-831 | 765-883 | 175.9 | 130-230
7- | 845 | 832-850 | 788-900 | 181.2 | 125-210
8- | 868 | 851-873 | 740-890 | 217.5 | 194-225
8+ | 870 | 861-884 | | |
--------+---------+----------+----------+---------+----------
| Females
+---------+----------+----------+---------+----------
1+ | 581 | | 415-658 | |
2- | 644 | 520-739 | 580-738 | 83.5 | 52-127
2+ | 743 | 685-804 | 670-826 | 135.2 | 73-200
3- | 810 | 740-829 | 730-880 | 149.4 | 98-219
3+ | 836 | 804-869 | 736-915 | 181.2 | 120-268
4- | 866 | 830-880 | 791-920 | 212.3 | 175-243
4+ | 883 | 870-914 | 810-952 | 191.2 | 143-300
5- | 914 | 880-929 | 833-1088 | 209.6 | 136-275
5+ | 932 | 915-954 | 883-990 | 250.4 | 195-336
6- | 965 | 930-961 | 892-1020 | 245.9 | 218-283
6+ | 970 | 955-980 | 885-1003 | 271 | 243-336
7- | 974 | 962-990 | 919-1050 | 251.3 | 150-330
7+ | 1000 | 980-1015 | 930-1085 | 295.6 | 235-375
--------+---------+----------+----------+---------+----------
A racer suddenly startled by close approach of a human usually flees
at high speed. The first part of its course, up to 20 feet or more, is
marked by a violent lateral thrashing of the body and tail, which may
help the snake to gain speed, but which seem chiefly designed to draw
attention of a potential attacker to the spot that the snake is
leaving. In any event, the mode of progression abruptly changes to a
swifter and much smoother travel, and the snake may seem to vanish
completely or as it glides rapidly away, its course may be marked by
the slowly waving tops of tall grass. The trend of travel away from
the site of disturbance is in an irregularly zig-zag course. The
method of crawling, with lateral undulations of the body, supported
against scattered pivot-points along the way, tends to prevent the
snake from moving more than a short distance in a straight line.
In checking traps along hilltop rock ledges in October, I have often
flushed racers that had come to the ledges searching for hibernation
dens. In such an instance the startled racer would usually dart away
down the steep slope at unusually high speed, and within a few seconds
might have covered 100 feet or more, progr
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