Part 1
# Natural History of the Racer Coluber constrictor ### By Fitch, Henry S. (Henry Sheldon)
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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.