Chapter 6

Fig. 20.Histograms comparing snout-vent length in random samples ofColuber c. flaviventris(those captured on the Reservation and Rockefeller Tract in 1960 and 1961) andC. c. mormon(specimens in the Museum of Vertebrate Zoology, University of California). In the museum sample, collected by conventional methods, the first-year young constitute a prominent and fairly distinct size group, whereas in the sample of racers from the Reservation and Rockefeller Tract, mostly caught in wire traps of quarter-inch mesh, relatively few young were secured. It is demonstrated that hatchlings are approximately the same length in both populations, butflaviventrisgrows much longer, and that the differences in length between the sexes is approximately the same in each population.

By assigning to each racer caught an arbitrary age, on the basis of size according toTable 17, I calculated the population (exclusive of those snakes in their first year of life) to have the composition shown inTable 19.

Table 19. Percentages of Adult Population of Blue RacersComprised by Each Annual Age Group

Figures are completely lacking to show the relative numbers of juveniles, until, already approaching adult size, the young are about to enter their second hibernation. My combined fall samples include 303 of these latter young, as against 142 racers about to enter their third hibernation. Thus, after having nearly attained adult size, these adolescent snakes sustained a loss of 53 per cent in a year. Losses must occur at an even more rapid rate in the younger and smaller snakes. It may be speculated that of the approximately 300 eggs produced by a population of 100 adult racers, 150 are lost before or during the period of incubation which lasts nearly two months. Of the 150 hatchlings emerging in early September, at least one-third probably are eliminated by the following breeding season in late May, leaving 100. The 100 survivors at this stage are still small juveniles, but by autumn they have attained adolescent size. By this time, if they had undergone a further reduction by 53 per cent, only 47 would remain—approximately the number to be expected if the population were stable from year to year.

A notable difference between the fall sample and the spring sample that I obtained was the higher proportion of large and old racers in the former sample. This difference can be attributed to the year-to-year changes in the population during the 14 consecutive years spanned by my field work. The fall sample of 734 racers represented the combined catch of the years 1949 through 1962, rather evenly distributed, but the spring sample included few snakes from the years 1949 through 1957; most were from the years 1958through 1961. In 1949 when the study was begun, the Reservation was being protected for the first time, and formerly overgrazed pastures or cultivated fields were acquiring a rank growth of grass and weedy vegetation, and thus becoming favorable habitat. The abundant new habitat promoted rapid increase in the population of racers until the newly available areas were filled to their "carrying capacity."Table 21shows the changing trends of the different age groups. Although the separate annual samples are perhaps too small to show the composition of the population accurately, it is significant that in the fall of 1949 an unusually high proportion of the racers caught were one-year-olds, hatched in September, 1948.

Table 20shows that in a typical group of 100 subadult and adult racers (second year and older) only a little more than one-fourth are productive females. The largest females, six years old and older, making up less than ten per cent of the adult population, contribute nearly half the total complement of eggs.

The calculated number of eggs pertains to a stage before oviposition, and subsequent losses through resorption under unfavorable conditions, through inviability of embryos and through deaths of some of the gravid females, are to be expected. In the weeks of incubation further losses are sustained. Although these losses cannot be measured, they must be severe as on numerous occasions scattered and torn eggshells representing entire clutches dug out and destroyed by predators, have been found. Probably other clutches are destroyed underground by such predators as moles and egg-eating snakes, and still others by insects. Tinkle (1959:195) wrote that in a clutch of 15 eggs found under a board, four were parasitized and had small perforations. Molds destroy a high percentage of all reptilian eggs that are incubated artificially and doubtless destroy many under natural conditions also. Excessive heat or moisture, or desiccation, resulting either from climatic extremes or from poor choice of a nest site by the female, would cause further loss. In four different years, Blair (1960:108) found that losses of eggs between laying and hatching in the Texas spiny lizard (Sceloporus olivaceus) ranged from 69 per cent to 86 per cent; no other comparable study of the extent of egg losses in a species of reptile is known to me. The racer is somewhat less prolific than the spiny lizard, and potentially longer lived; the racer's eggs are larger and thicker-shelled, and they are deposited in deeper burrows. It might be expected that losses during incubation would be somewhat less in the racer than in the spiny lizard.

Table 20. Calculated Productivity in a Hypothetical Group of 100 Subadult and Adult Blue Racers

Table 21. Percentages of Racers in Each Annual Age Group (Exclusive of Hatchlings)in Autumnal Samples at Different Stages of the Field Study,Showing Shift Toward Older Age-Groups in the Later Years

Although figures for the youngest age groups—one-year-olds and hatchlings—are missing, approximations of them may be furnished by extrapolation, from the information available regarding the productivity of the population. Some factors involved in productivity are that the sex ratio deviates from parity, slightly in favor of the females in the adolescents but more markedly in favor of the females among the older age groups; that some adult females apparently fail to produce eggs in the breeding season, but the percentage decreases in the older snakes; and that number of eggsper clutch increases in proportion to the size and age of the female producing them. Too few figures are available concerning most of these factors to indicate more than the trends; nevertheless the available figures have been used inTable 20in an attempt to estimate the productivity of a hypothetical population.

Numbers

Conant (1938:178, Pl. 7) published a photograph of 106 blue racers killed in February, 1932, by farmers near Bellville, Ohio, and Pope (1944:173) mentioned that scores of blue racers aggregated in October around an oak-covered dune near Chicago. In both these instances large hibernating aggregations were involved, and the areas represented by them are unknown; nothing has been recorded regarding population densities.

The records obtained through my fall trapping, along hilltop rock outcrops, yielded no information concerning population densities, but those obtained in fields in summer did provide significant information in this regard. Even after years of trapping on the same area, the catch still consisted largely of new individuals; the method was not sufficiently effective to catch all racers present at any one time, and the total catch for a season therefore provided only a crude index of the minimum number present.

The summer trapping was carried on in three separate areas. One of these was the area of bottomland pastures and formerly cultivated fields where the Reservation headquarters are located, a block of 39 acres bounded on three sides by woodland, and on the fourth by cultivated farm land. Effective trapping in this area was carried on through the years 1955 to 1961 inclusive. A second area, of 48 acres, was one of upland fields, mostly covered with re-established prairie grasses, in the northeastern part of the Reservation. A third area, of 137 acres, also upland, was that of the Rockefeller Tract, cultivated through 1956 and sown to prairie grasses the following year, and the adjacent northwestern hilltop portion of the Reservation. Effective trapping on these two latter areas was carried on in 1958 through 1962.

For the seven years of trapping in the House Field area, the catch was as follows: 30, 33, 38, 38, 34, 24, and 20. In four years of trapping, the northeast field area yielded 42, 28, 37, 59, and 19 blue racers, and the Rockefeller Tract yielded 52, 67, 67, 126, and 106. The actual catch was hence less than one per acre in nearly all instances, but the year-to-year differences in catch are believedto be caused chiefly by differences in numbers of traps used and in trapping effort, rather than by changes in the numbers of racers present.

Best index to the number of racers actually present is provided by the number of recaptures, and their ratio to first captures. The population of course, undergoes alteration from year to year, with many racers eliminated and replaced by others.

In 1955, 26 racers were caught in the May-June-July period, in the headquarters field area. In the August-September-October period of the same year five racers were caught of which only one was a member of the original 26. The five-to-one ratio indicates that the original 26 may have represented an actual population of 130, but of course the single recapture is much too small a sample to provide a reliable ratio. Some of the racers caught in May were recaptured in June, others in July, and still others not until late summer or early autumn. Somewhat different estimates can be obtained for the population depending on how the season's records are divided. For instance, in the headquarters field area in May 1955, eleven racers were caught; in the remainder of the season 20 were caught, of which two were members of the original group of eleven. The 20 to 2 ratio indicates that the 11 caught in May represented an actual population of 110. In the period May-June, 18 racers were caught, and in July-August-September-October, 15 were caught, including four of the original 18, hence indicating a population of 67. Although obviously the population underwent some change during the course of the season, the three sets of census figures apply essentially to the same population, and the divergence in them illustrates thewide range of error arising from insufficiently small samples.

Common sources of error in the censusing of natural populations of animals by the capture-recapture method ("Lincoln Index" or "Petersen Index") arise from the fact that the composition of a local population often changes between two sampling periods, or even within them. Some of the animals marked may move elsewhere, to be replaced by unmarked immigrants, or they may die and be replaced by unmarked maturing young. First-year racers that could pass through the quarter-inch mesh of the traps in spring and early summer became too large to escape in this way in the latter half of the summer, but these young were excluded from the census computations. There was doubtless some shifting of marked individuals away from the study areas and shifting of new individuals ontothese areas in the periods of weeks between successive samplings. Jackson (1939) has explained a method of correcting census computations based on capture-recapture ratios when there is a consistent trend of diminishing recaptures with increase in elapsed time. However, in my records no such trend is discernible; furthermore it has been demonstrated that individual racers tend to stay within the same home range area throughout most of their season of activity. Therefore, I conclude that shifts of individuals away from the study areas or into them, in the intervals between samplings constitute only a minor source of error.

A combination of the figures from the three samples listed above provides an intermediate "smoothed" figure that can be accepted with somewhat more confidence than any one of the separate censuses because it is based on more records. The combined ratios indicate a total of 105 racers in the headquarters field area. The figures obtained in the different sampling periods, and the census figures derived from their ratios are shown in tables 22 and 23. Differences from year-to-year in the census figures for any one area show no consistent trends and their variation is similar to that shown in different samples for the same season. Probably populations were fairly stable throughout the periods involved. If such stability is assumed, the samples from different years may be combined, and the composite figures derived from them may be accepted with more confidence. For the headquarters field area, for instance, 419 records of racers were gathered in all the preliminary sampling periods of the seven seasons involved; the records totalled 263 for all the secondary sampling periods, with 70 recaptures in secondary periods of the snakes recorded in the corresponding preliminary periods. A population of 75 racers is indicated—1.9 per acre. Corresponding figures for the northeast field area are: preliminary samples 453, secondary samples 163, recaptures 39, calculated number 135 (2.82 per acre). For the Rockefeller Tract the figures are as follows: Preliminary samples 807, secondary samples 476, recaptures 126, the ratio indicating a population of 153, or 1.11 per acre.

These figures represent the number of adults present in early summer when the population is near its annual low point. The first-year young, excluded from this census because they cannot be caught in representative numbers, perhaps approximate the number of adults, in May, so the figures obtained would need to be approximately doubled to be representative of the entire population.By late summer the adults, and especially the yearlings, have undergone substantial reduction in numbers, but in late August and early September the hatching of a new crop of young increases the population to its annual maximum. The maximum numbers probably are about three times those obtained by censusing adults in early summer. The peak population of late summer or early autumn is estimated to consist of hatchlings, comprising somewhere near 50 per cent; adults, comprising a little more than 25 per cent; and yearlings comprising a little less than 25 per cent.

Table 22. Captures Recorded and Population Calculated From Themon Hilltop Grassland Areas of Rockefeller Experimental Tractand Adjacent Reservation in Four Different Years

Densities in early summer of one to three adult blue racers peracre probably are typical of the better types of habitat in the region of my study. The upland field area estimated to have 2.82 racers per acre was better habitat than the other two study areas. Prior to 1948 it had been cultivated and severely eroded. In 1949 most of it was sown to seeds of prairie grasses, and by 1958 different parts of it were dominated by different species of native perennial tall grasses interspersed with areas that supported a weedy type of vegetation, and other areas that supported dense thickets of sumac, dogwood, elm saplings, or other woody plants. The abundance and diversity of dense cover and of small animals made this area especially favorable habitat for the racer.

Table 23. Captures Recorded and Populations Estimated From Themin Headquarters Field Area of Reservation

PLATE 19Fig. 1.Head of hatchling blue racer, dorsal view, September 1962, approximately × 3.Fig. 2.Head of hatchling blue racer, lateral view, September 1962, approximately × 3.Fig. 3.Head of yearling male blue racer, lateral view, August 1, 1961, a little less than twice natural size.Fig. 4.Head of adult male blue racer, lateral view, July 16, 1961, approximately × 2. All three snakes from Rockefeller Experimental Tract, Jefferson County, Kansas.

PLATE 19

Fig. 1.Head of hatchling blue racer, dorsal view, September 1962, approximately × 3.

Fig. 2.Head of hatchling blue racer, lateral view, September 1962, approximately × 3.

Fig. 3.Head of yearling male blue racer, lateral view, August 1, 1961, a little less than twice natural size.

Fig. 4.Head of adult male blue racer, lateral view, July 16, 1961, approximately × 2. All three snakes from Rockefeller Experimental Tract, Jefferson County, Kansas.

PLATE 20

Fig. 1.Abandoned limestone quarry on a hilltop of southward exposure on The University of Kansas Natural History Reservation, in late autumn of 1951. The crevices along the base of the ledge provided favorite hibernating sites for blue racers.

Fig. 2.Hatchling blue racer and eggshell from which it had recently emerged, in early September, 1962; × approximately 12/3.

PLATE 21

Fig. 1.Wire funnel trap set at base of hilltop limestone outcrop in a spot strategically located for interception of blue racers searching for deep crevices in which to hibernate, October 15, 1949.

Fig. 2.Large clutch of 21 blue racer eggs, recently plowed out, at Harold Brune farm, Jefferson County, Kansas, July 10, 1962.

PLATE 22

Fig. 1.Habitat of blue racer, blue-stem prairie on Botany Bluff at northwest corner of the University of Kansas Natural History Reservation, looking south. Trees and brush in background are along limestone outcrop at top of slope. Mowed area in foreground is southwest corner of Rockefeller Experimental Tract, a privately owned farm at the time this photograph was taken in the summer of 1951.

Fig. 2.Habitat of blue racer, blue-stem prairie on south slope of Botany Bluff, looking north along west edge of the Reservation, summer of 1951. By 1962, with exclusion of fire, and protection from mowing, prairie vegetation had largely disappeared from this slope, and had been replaced by trees and brush. As a result of these successional changes racers no longer found this slope a suitable habitat in summer, but they continued to resort to the hilltop rock outcrop to hibernate in autumn.

Some local areas probably support higher populations of racers than do areas where censuses were made, but under modern conditions, situations that offer near optimum habitat are not likely to be extensive or to persist long. On land that is capable of producing a good crop of vegetation, the crop is usually harvested either by grazing of livestock or by using the land for cultivation, with the result that the racers are, at least in some seasons, forced into marginal situations. More than 50 years ago in Missouri, Hurter (1911:170) wrote that the racer "was quite common 20 years ago in pastures, meadows and fields but as cultivation has advanced it is becoming quite rare." In 1962 the widespread and adaptable blue racer is still common in many parts of its range, including Missouri, but in most places its population densities probably are lower than formerly.

Reduction since 1911 has probably been far more drastic than the reduction that had occurred up to that time. Schmidt and Necker (1935:69), writing of the racer in the Chicago region, noted "the snakes which raise their heads and face mowing machinery tend to be exterminated in agricultural areas." They stated that in the Chicago region the racer had been exterminated by the advance of agriculture except in two extensive sand dune areas. In July 1962, Mr. V. B. Howell, a progressive farmer of the Great Bend area in central Kansas, told me that the kinds of snakes inhabiting cultivated land—blue racer, bull snakes, prairie king snakes, hog-nosed snakes, and others—had undergone great reduction in numbers during the period of his farming. He estimated that in a forty-year period the numbers had declined to perhaps five per cent of their level in the area most familiar to him, centering at his farm 11 miles northwest of Great Bend, Barton County. In accounting for this change in population density Howell pointed out the relative destructiveness to small animals of modern farm machinery as contrasted with horse-drawn equipment or that used with tractors of earlier models. Modern tractors move forward so rapidly that there is little opportunity for snakes or other small animals to avoid them, and the plows and disks cut wide swaths penetrating more deeply into the soil than did older types. On July 10, 1962, in searching the furrows of a freshly plowed small field on the Harold Brune farm, for turned-up nests of the snakes, I found two adult blue racers that had been struck and killed by the plow, possibly while they were underground. In fields that are plowed or cultivated between the times of egg-laying and hatching, the eggs are destroyed. Because of its rapid movements and alertness, the raceris more likely to escape farm machines than are most other kinds of snakes. Nevertheless, it is vulnerable and survives in cultivated areas only when they are interspersed with pastures, woodlots, or streamside thickets where at least part of the population may find refuge.

Summary

Field study of the blue racer was carried on in several localities in Kansas, but chiefly at the University of Kansas Natural History Reservation (the northeasternmost section of land in Douglas County), and the adjacent 160-acre Rockefeller Experimental Tract in Jefferson County. By October 26, 1962, after 14 years of field work, a total of 1423 racers had been captured some 2197 times.

The locale of the present study was near the geographic center of the blue racer's range. The range, chiefly in the Mississippi Valley and Great Plains region, is centrally situated with respect to the other seven subspecies. An extensive but scattered literature concerning the ecology of the species as a whole, and its several geographic races, has been reviewed and utilized for comparison with my own field data.

Blue racers were caught in wire funnel traps set in prairie and pastureland habitat in summer, and along hilltop limestone outcrops in woodland in autumn. The autumn trapping along rock outcrops was carried on each year from 1949 to 1962, but effective summer trapping was carried on only in the last six years of the study. Each racer caught was individually and permanently marked by scale clipping. More than half were caught only once, but many were recorded repeatedly, with a maximum of 16 captures.

The racer occurs throughout most of the United States, and its populations are subject to much geographic variation. The snakes are largest in the northeastern part of the range, with clines of decreasing size toward the southeastern, southern and western parts of the United States. There are somewhat parallel trends in coloration; the black racer of the northeastern states grades into paler, gray or light brown subspecies in southern Florida, Texas, and the far western states. Accompanying these changes in color and size are minor morphological changes and major ecological changes. The black racers of the eastern states often inhabit forest or forest-edge habitats while the paler and smaller snakes of more southern or western areas typically inhabit scrub, chaparral, or prairie. The large, dark-colored racers of the eastern and northeastern states are especially inclined to attack larger prey including small vertebrates,even weasels, rabbits, and chipmunks, whereas the smaller and paler racers of more southern and more western areas take a higher proportion of insects and rarely attack vertebrates other than small reptiles.

On the area where field work was carried on in northeastern Kansas, tall-grass prairie habitat is preferred, but fields of grain or alfalfa, grazed pasture, brush, woodland edge, groves or open woodland, and weedy fields are all utilized to some extent. The racer is strictly diurnal and largely terrestrial but it may climb through bushes or small trees in foraging or escaping.

The blue racer is a typical colubrine snake of slender build, with large eyes, and vision plays an important role in finding prey and detecting enemies. In the adult blue racer the dorsal color is variable, pale brown or gray, bluish, greenish or slaty. In the hatchling, however, there is a distinct pattern of a type widespread among colubrines and also among snakes of other groups—a series of middorsal blotches on an olive ground color, with alternating rows of smaller spots on each side. The ventral surface is pale, with dark speckling. The pattern is sharply defined on the anterior part of the body, but markings become progressively more obscure posteriorly and are scarcely discernible on the tail.

The juvenal pattern fades gradually as growth proceeds, and there is much individual variation in the rate of its loss. Some racers still retain the juvenal pattern faintly discernible after attainment of sexual maturity. There are also striking ontogenetic changes in the proportions of the head, body and tail. The diameter of the eye is approximately one per cent of the snout-vent length in hatchlings, but is only a little more than half that relative size in the largest adults. In the course of allometric growth other parts of the head also enlarge less rapidly than the body, but more rapidly than the eye. In hatchlings there is a slight average difference between the sexes in relative tail length, with males' tails the longer. Relative tail length increases slightly in both sexes up to the time of sexual maturity, and then decreases slightly with advancing age.

Racers in northeastern Kansas spend nearly half the year in hibernation, with average recorded emergence date April 16, and average date of retirement into hibernation November 8. Hibernacula are usually in crevices in hilltop limestone outcrops with south exposures. Winter temperatures within the hibernacula are usually well within the range 0 degrees to 10 degrees Centigrade. Springemergence has been recorded at an air temperature of only 12.5 degrees Centigrade. Racers bask in sunshine frequently even in warm weather, and the temperature preferendum is several degrees higher than in most other kinds of snakes. Bodily temperatures obtained from blue racers that were fully active, either under natural conditions or in a large outdoor enclosure, were concentrated in the neighborhood of 34 and 35 degrees Centigrade. For short periods racers can survive temperatures up to 45 degrees without damage, but more prolonged exposure to temperatures of slightly less than 40 degrees can be fatal. In hibernation, racers can withstand temperatures slightly below freezing, but they cannot survive being frozen solid.

Blue racers tend to limit their activities to familiar areas or home ranges; some individuals may live out their entire lives within the same home range, but others shift from time to time. Average home ranges of approximately 26 acres for males and 24 acres for females were calculated. The racers' preference for hibernacula in a habitat different from that to which summer activities are confined necessitates spring and fall migrations between the limestone outcrops where hibernation occurs and the grasslands where the snakes stay in summer. The average spring or fall migration is approximately a quarter of a mile, but an individual racer does not consistently return to the same hibernaculum. Many racers were recorded to have made movements of 2000 to nearly 4000 feet, involving shifts in home range, but some later shifted back to their original areas. Some may have made even longer shifts but their movements would not have been recorded since they would have gotten beyond the limits of the study area.

Blue racers hunt by various methods, often by coursing through dense vegetation in active search in which vision is of primary importance in locating the prey. Almost any small animal that moves nearby may be overtaken and caught with a sudden dash. From analysis of scats and prey from stomachs, a total of 1357 food items of more than 50 species was compiled. Favorite prey species were the cricket (Gryllus assimilis), grasshoppers (Arphia simplex,Melanoplus femur-rubrum,M. bivittatus,M. differentialis), camel crickets (Ceuthophilussp.), katydid (Neoconocephalus robustus), vole (Microtus ochrogaster), white-footed mouse (Peromyscussp.), racerunner, (Cnemidophorus sexlineatus), and leopard frog (Rana pipiens). The insects taken greatly outnumbered the vertebrates, but the vertebrates made up most of the actual bulk of prey eaten.Crickets, grasshoppers, and katydids comprised most of the insect prey. Beetles, moths and cicadas were rarely taken. Vertebrate prey included miscellaneous small snakes (some of them juvenal racers), mammals, and birds. Seasonal change in the composition of the food is slight, but vertebrates figure more prominently in early summer, and insects comprise increasing percentages later in the season. Composition of the food differs according to size of the snake; gryllid and ceuthophilid crickets are best represented in the food of juveniles whereas small mammals, and grasshoppers of the genusMelanoplusare best represented in the food of large adults.

The breeding season is mainly in May. Mating is promiscuous and two or more males may court the same female simultaneously. A courting male lies on or alongside a receptive female, with spasmodic rippling abdominal movements, and with his vent adpressed to hers. At intervals in the courtship period the female moves swiftly for a few feet or a few yards shifting to a new spot, and during her activity the male strives to maintain contact with her. From time to time the male leaves the female briefly and courses rapidly around her in a devious route. Courtship is consummated when the female raises her tail in acceptance of the male and intromission is effected. During coitus, which lasts for periods of minutes, the female moves forward slowly, dragging the passive male, tail-first behind her.

Ovulation normally is in late May. Eggs from 29 to 39 millimeters in length and 14 to 21 millimeters in breadth are laid, from mid-June to early August, usually in tunnels of fossorial mammals such as voles or moles, at depths of five to 12 inches. Clutches of the blue racer average 11.8 eggs but the number is correlated with age and size of females; two-year-olds average only 9.2 eggs, whereas those females that are six years old or more average 15.7 eggs. Also, there is geographic variation in size of clutch, from only 5.8 eggs inC. c. mormonof the West Coast to 16.8 eggs inC. c. constrictorof the northeastern states. In each breeding season some females of adult size do not produce clutches. Only about 13 per cent of the two-year-olds in a small sample were fecund, but the ratio increased to 80 per cent in old adults. Incubation averages 51 (43 to 63) days.

Hatchlings usually make several longitudinal slits in the eggshell with the egg tooth before emerging, and often require a day or more to emerge after the first slit is made. Hatchlings average103/4inches and 4.16 grams. By late October when these young are ready to enter hibernation, they have grown to 163/4inches and 12.3 grams. Typical October lengths (overall) in inches for males and females, respectively, after successive seasons of growth, are as follows: yearlings, 273/4and 29; two-year-olds, 341/4and 371/4; three-year-olds, 373/4and 413/4; four-year-olds, 40 and 443/4; five-year-olds, 411/2and 461/4; six-year-olds, 421/4and 481/4; seven-year-olds, 433/4and 50; eight-year-olds, 44 and 511/4.

Judging from trends in the small samples available, sex ratio in hatchlings is approximately 1:1. In the summer trapping of blue racers, males are caught in larger numbers than females, but seemingly this is because of their greater activity. In fall along the limestone outcrops where the racers hibernate females were caught in slightly greater numbers than males among the young adults, and made up a little more than 60 per cent of the old adults. Presumably the males are eliminated more rapidly, because of their greater activity, their smaller size, or a combination of both factors. The composition by age groups of the adult racers captured was as follows: two-year-olds, 41.5 per cent; three-year-olds, 17.8 per cent; four-year-olds, 12.6 per cent; five-year-olds, 9.5 per cent; six-year-olds, 6.1 per cent; seven-year-olds, 4.3 per cent; eight-year-olds, 2.7 per cent; nine-year-olds, 2.4 per cent; ten-year-olds, 1.2 per cent; more than ten years old, 1.9 per cent.

Attempts to census blue racers on the study plots, from the capture-recapture ratios, yielded highly variable figures for different areas and even for the same area at different times. Variability is believed to result mostly from the small sizes of the samples, none of which is large enough to yield a census figure that is statistically reliable. Combined samples yielded figures indicating populations of one to three adults per acre in early summer in areas of favorable habitat. To represent the entire population in late summer—the time of its annual maximum—these figures would need to be approximately tripled.

The blue racer depends mostly on speed to escape its enemies. In escaping it often takes advantage of a downhill slope to increase its speed. A racer startled at close range often sets out with a violent thrashing that attracts attention to a given spot, then glides away so silently and rapidly that its course is not detected. The snake may circle back and approach the scene of disturbance slowly and stealthily, from the direction opposite to that taken in departing. Often a racer seeks concealment by climbing into a bush ortree, and occasionally escape is effected by swimming. A racer that is caught or cornered usually makes a spirited defense by striking and biting. An alternative reaction, seen most typically when the snake is handicapped by injury or by low temperature, is to coil with the head concealed, and, with writhing movements, to smear the surface of the body with musk discharged from glands in the base of the tail.

Many natural enemies prey upon the racer, but in the present study the majority of records pertained to the red-tailed hawk. The broad-winged hawk, marsh hawk, red-shouldered hawk, sparrow hawk, and barn owl also are among the raptors that feed on this kind of snake. Among mammals the striped skunk is the only species definitely recorded to prey on the racer, feeding on the eggs as well as upon the young and adults. The common king snake, prairie king snake, timber rattlesnake, copperhead, and even the slender glass lizard have been recorded to prey on the blue racer, but probably all are of minor importance as natural enemies. Shrews (Blarina,Cryptotis) and mice (Peromyscus,Reithrodontomys) have sometimes killed and eaten racers confined in traps, and under natural conditions they possibly prey upon snakes that are immobilized when torpid from cold, in their hibernacula and temporary shelters. Chiggers are the most common ectoparasites of the racers. Four species of the chigger genusTrombiculahave been recorded on racers from the Reservation. The racer is an important host of the common pest chigger,Trombicula alfreddugèsi, which often attacks humans. Most adult racers on the Reservation and nearby areas carry the fluke,Neorenifer lateriporus. In spring these flukes are conspicuous in the mouths of the racers, but in late summer they are not in evidence.

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1933. A method of marking living snakes for future recognition with a discussion of some problems and results. Ecology, 14:334-349.

Bogert, C. M.andCowles, R. B.

1947. Moisture loss in relation to habitat selection in some Floridian reptiles. Results of the Archbold Expeditions, No. 58; Amer. Mus. Novit., 1358:1-34.

Bonn, E. W.andMcCarley, W. H.

1953. The amphibians and reptiles of the Lake Texoma area. Texas Jour. Sci., 1953(4):465-471.

Boyer, D. A.andHeinze, A. A.

1934. An annotated list of the amphibians and reptiles of Jefferson County, Missouri. Trans. Acad. Sci. St. Louis, 28(4):183-200.

Branson, E. B.

1904. Snakes of Kansas. Univ. Kansas Sci. Bull., 12(13):353-430.

Brattstrom, B. H.

1953a. Records of Pleistocene reptiles and amphibians from Florida. Quart. Jour. Florida Acad. Sci., 16(4):243-248.1953b. The amphibians and reptiles from Rancho La Brea. Trans. San Diego Soc. Nat. Hist., 11(14):365-392.1955. Pliocene and Pleistocene amphibians and reptiles from southeastern Arizona. Jour. Paleontology, 29(1):150-154.

1953a. Records of Pleistocene reptiles and amphibians from Florida. Quart. Jour. Florida Acad. Sci., 16(4):243-248.

1953b. The amphibians and reptiles from Rancho La Brea. Trans. San Diego Soc. Nat. Hist., 11(14):365-392.

1955. Pliocene and Pleistocene amphibians and reptiles from southeastern Arizona. Jour. Paleontology, 29(1):150-154.

Breckenridge, W. J.

1944. Reptiles and amphibians of Minnesota. Univ. Minnesota Press, 202 pp.

Brimley, C. M.

1903. Notes on the reproduction of certain reptiles. Amer. Nat., 37:261-266.

Brons, H. A.

1882. Notes on the habits of some western snakes. Amer. Nat., 16:564-567.

Brumwell, M. J.

1951. An ecological survey of the Fort Leavenworth Military Reservation. Amer. Midl. Nat., 45(1):187-231.

Burt, C. E.

1927. An annotated list of the amphibians and reptiles of Riley County, Kansas. Occas. Papers Mus. Zool. Univ. Michigan, 189:1-9.1933. Some distributional and ecological records of Kansas reptiles. Trans. Kansas Acad. Sci., 36:186-208.1935. Further records of the ecology and distribution of amphibians and reptiles in the Middle West. Amer. Midl. Nat., 16(3):311-336.

1927. An annotated list of the amphibians and reptiles of Riley County, Kansas. Occas. Papers Mus. Zool. Univ. Michigan, 189:1-9.

1933. Some distributional and ecological records of Kansas reptiles. Trans. Kansas Acad. Sci., 36:186-208.

1935. Further records of the ecology and distribution of amphibians and reptiles in the Middle West. Amer. Midl. Nat., 16(3):311-336.

Burt, C. E.andHoyle, W. L.

1934. Additional records of the reptiles of the central prairie region of the United States. Trans. Kansas Acad. Sci., 37:193-216.

Cagle, F. R.

1942. Herpetological fauna of Jackson and Union counties, Illinois. Amer. Midl. Nat., 28(1):164-200.

Carpenter, C. C.

1958. Reproduction, young, eggs and food of Oklahoma snakes. Herpetologica, 14:113-115.

Carr, A. F. Jr.

1940. A contribution to the herpetology of Florida. Univ. Florida Publ. Biol. series, 3:iv + 118 pp.

Clark, R. F.

1949. Snakes of the hill parishes of Louisiana. Jour. Tennessee Acad. Sci., 24(4):244-261.

Clarke, R. F.

1958. An ecological study of reptiles and amphibians of Osage County, Kansas. Emporia State Research Studies, 7(1):1-52.

Cohen, E.

1948. Emergence ofColuber c. constrictorfrom hibernation. Copeia, 1948:137-138.

Committee on Herpetological Common Names

1956. Common names for North American amphibians and reptiles. Copeia, 1956(3):172-185.

Conant, R.

1938. The reptiles of Ohio. Amer. Midl. Nat., 20(1):1-200.1958. A field guide to reptiles and amphibians of the United States and Canada east of the 100th Meridian. Houghton-Mifflin Co., Boston xviii + 366 pp., 40 pls., 62 figs., 248 maps.

1938. The reptiles of Ohio. Amer. Midl. Nat., 20(1):1-200.

1958. A field guide to reptiles and amphibians of the United States and Canada east of the 100th Meridian. Houghton-Mifflin Co., Boston xviii + 366 pp., 40 pls., 62 figs., 248 maps.

Cope, E. D.

1900. The crocodilians, lizards and snakes of North America. Rept. U. S. Nat. Mus. for 1898, pp. 153-1270.

Crabb, W. D.

1941. Food habits of the prairie spotted skunk in southeastern Iowa. Jour. Mamm., 22(4):349-364.

Crow, H. E.

1913. Some trematodes of Kansas snakes. Univ. Kansas Sci. Bull., 7:123-134.

Cunningham, J. D.

1959. Reproduction and food of some California snakes. Herpetologica, 15(1):17-19.

Curtis, L.

1949. The snakes of Dallas County, Texas. Field & Laboratory, 17:5-13.

Dice, L. R.

1916. Distribution of the land vertebrates of southeastern Washington. Univ. California Publ. Zool., 16(17):293-348.

Ditmars, R. L.

1896. The snakes found within fifty miles of New York City. Abs. Proc. Linn. Soc. New York, 8:9-24.1907. The reptile book. Doubleday, Page and Co., New York, pp. xx + 472.1944. Serpents of the northeastern states. New York Zool. Soc., 34 pp., 21 pls.

1896. The snakes found within fifty miles of New York City. Abs. Proc. Linn. Soc. New York, 8:9-24.

1907. The reptile book. Doubleday, Page and Co., New York, pp. xx + 472.

1944. Serpents of the northeastern states. New York Zool. Soc., 34 pp., 21 pls.

Duellman, W. E.

1951. Notes on the amphibians and reptiles of Greene County, Ohio. Ohio Jour. Sci., 51(6):335-341.

Duellman, W. E.andSchwartz, A.

1958. Amphibians and reptiles of southern Florida. Bull. Florida State Mus. Biol. Sci., 3(5):181-324.

Ellicott, E. L.

1880. Bundles of snakes. Am. Nat., 14:206-207.

Etheridge, R. E.

1952. The southern range of the racerColuber constrictor stejnegerianus(Cope), with remarks on the Guatemalan speciesColuber ortenburgeriStuart. Copeia, 1952:189-191.

Ferguson, D. E.

1952. The distribution of amphibians and reptiles of Wallowa County, Oregon. Herpetologica, 8:66-68.

Finneran, L. C.

1948. Reptiles at Branford, Connecticut. Herpetologica, 4:123-126.

Fitch, H. S.

1935. Natural history of the alligator lizards. Trans. Acad. Sci. St. Louis, 29(1):1-38.1936. Amphibians and reptiles of the Rogue River Basin, Oregon. Amer. Midl. Nat., 17(3:634-652).1940. A biogeographical study of the ordinoides artenkreis of garter snakes (genus Thamnophis). Univ. California Publ. Zool., 44(1):1-150.1949. Road counts of snakes in western Louisiana. Herpetologica, 5:87-90.1951. A simplified type of funnel trap for reptiles. Herpetologica, 7:77-80.1954. Life history and ecology of the five-lined skink,Eumeces fasciatus. Univ. Kansas Publ. Mus. Nat. Hist., 8(1):1-156.1955. Habits and adaptations of the Great Plains skink. Ecol. Monogr., 25(3):59-83.1956. Temperature responses in free-living amphibians and reptiles of northeastern Kansas. Univ. Kansas Publ. Mus. Nat. Hist., 8(7):417-476.1958. Home ranges, territories and seasonal movements in vertebrates of the Natural History Reservation. Univ. Kansas Publ. Mus. Nat. Hist. 11(3):63-326.1960. Autecology of the copperhead. Univ. Kansas Publ. Mus. Nat. Hist., 13(4):85-288.

1935. Natural history of the alligator lizards. Trans. Acad. Sci. St. Louis, 29(1):1-38.

1936. Amphibians and reptiles of the Rogue River Basin, Oregon. Amer. Midl. Nat., 17(3:634-652).

1940. A biogeographical study of the ordinoides artenkreis of garter snakes (genus Thamnophis). Univ. California Publ. Zool., 44(1):1-150.

1949. Road counts of snakes in western Louisiana. Herpetologica, 5:87-90.

1951. A simplified type of funnel trap for reptiles. Herpetologica, 7:77-80.

1954. Life history and ecology of the five-lined skink,Eumeces fasciatus. Univ. Kansas Publ. Mus. Nat. Hist., 8(1):1-156.

1955. Habits and adaptations of the Great Plains skink. Ecol. Monogr., 25(3):59-83.

1956. Temperature responses in free-living amphibians and reptiles of northeastern Kansas. Univ. Kansas Publ. Mus. Nat. Hist., 8(7):417-476.

1958. Home ranges, territories and seasonal movements in vertebrates of the Natural History Reservation. Univ. Kansas Publ. Mus. Nat. Hist. 11(3):63-326.

1960. Autecology of the copperhead. Univ. Kansas Publ. Mus. Nat. Hist., 13(4):85-288.

Fitch, H. S.andPackard, R. L.

1955. The coyote on a natural area in northeastern Kansas. Trans. Kansas Acad. Sci., 58:211-221.

Fitch, H. S.andSandidge, L. L.

1953. Ecology of the opossum on a natural area in northeastern Kansas. Univ. Kansas Publ. Mus. Nat. Hist., 7(2):305-338.

Force, E. R.

1930. The amphibians and reptiles of Tulsa County, Oklahoma, and vicinity. Copeia, 1930(2):25-39.

Fouquette, M. J.andLindsay, H. L., Jr.

1955. An ecological survey of reptiles in parts of northwestern Texas. The Texas Jour. Sci., 7(4):402-421.

Gloyd, H. K.

1928. The amphibians and reptiles of Franklin County, Kansas. Trans. Kansas Acad. Sci., 31:115-141.1932. The herpetological fauna of the Pigeon Lake region, Miami County, Kansas. Papers Michigan Acad. Sci. Arts and Letters, 15:389-409.1945. The problem of too many snakes. Chicago Nat., 7(4):87-97.

1928. The amphibians and reptiles of Franklin County, Kansas. Trans. Kansas Acad. Sci., 31:115-141.

1932. The herpetological fauna of the Pigeon Lake region, Miami County, Kansas. Papers Michigan Acad. Sci. Arts and Letters, 15:389-409.

1945. The problem of too many snakes. Chicago Nat., 7(4):87-97.

Grinnell, J.,Dixon, J., andLinsdale, J. M.

1930. Vertebrate natural history of a section of northern California through the Lassen Peak region. Univ. Calif. Publ. Zool., 35: v + 594 pp., 181 figs.

Guidry, E. V.

1953. Herpetological notes from southeastern Texas. Herpetologica, 9:49-56.

Hamilton, W. J., Jr., andPollack, J. A.

1956. The food of some colubrid snakes from Fort Benning, Georgia. Ecology, 37:519-526.

Harwood, P. D.

1933. The helminths parasitic in the Amphibia and Reptilia of Houston, Texas and vicinity. Proc. U. S. Nat. Mus., 81, 17:1-71.

Hay, O. P.

1893. On the breeding habits, eggs, and young of certain snakes. Proc. U. S. Nat. Mus., 15:385-397.

Hibbard, C. W.

1936. The amphibians and reptiles of Mammoth Cave National Park Proposed. Trans. Kansas Acad. Sci., 39:277-281.

Hudson, G. E.

1942. The amphibians and reptiles of Nebraska. Nebraska Conservation Bull. no. 24, 146 pp.

Hudson, R. G.

1949. A record length milk snake. Herpetologica, 5:47.

Hurter, J. H.

1911. Herpetology of Missouri. Trans. Acad. Sci. St. Louis, 20:59-274.

Inger, F.andClark, P. J.

1943. Partition of the genusColuber. Copeia, 1943(3):141-145.

Jackson, C. H. N.

1939. The analysis of an animal population. Jour. An. Ecology, 8:238-246.

King, W.

1939. A survey of the herpetology of Great Smoky Mountain National Park. Amer. Midl. Nat., 21(3):531-582.

Klimstra, W. D.

1959. Food of the racer,Coluber constrictor, in southern Illinois. Copeia, 1959(3):210-214.

Langbartel, D. A.

1947. Snakes collected at Camp Eastman, Hancock County, Illinois. Herpetologica, 4:27-28.

Liner, E. A.

1949. Notes on the young of the blue racer,Coluber constrictor flaviventris. Copeia, 1949(3):230.1954. The herpetofauna of Lafayette, Terrebonne, and Vermilion parishes, Louisiana. Proc. Louisiana Acad. Sci., 17:65-85.1955. A herpetological consideration of the Bayou Tortue region of Lafayette Parish, Louisiana. Proc. Louisiana Acad. Sci. 18:39-42.

1949. Notes on the young of the blue racer,Coluber constrictor flaviventris. Copeia, 1949(3):230.

1954. The herpetofauna of Lafayette, Terrebonne, and Vermilion parishes, Louisiana. Proc. Louisiana Acad. Sci., 17:65-85.

1955. A herpetological consideration of the Bayou Tortue region of Lafayette Parish, Louisiana. Proc. Louisiana Acad. Sci. 18:39-42.

Linsdale, J. M.

1927. Amphibians and reptiles of Doniphan County, Kansas. Copeia, no. 164:75-81.

Loewen, S. I.

1940. On some reptilian cestodes of the genus Oochoristica (Anoplocephalidae). Trans. Amer. Microscop. Soc., 59(4):511-518.

Logier, E. B. S.

1932. Some account of the amphibians and reptiles of British Columbia. Contr. Royal Ontario Mus., Trans. Royal Canadian Inst., 18(2):311-336.

Loomis, R. B.

1956. The chigger mites of Kansas (Acarina, Trombiculidae). Univ. Kansas Sci. Bull., 37, pt. 2(19):1195-1443.

Lord, J. K.

1866. The naturalist in Vancouver Island and British Columbia. Richard Bentley, London, 375 pp.

Marr, J. C.

1944. Notes on amphibians and reptiles from the central United States. Amer. Midl. Nat., 32:478-490.

Martin, E. P.

1956. A population study of the prairie vole (Microtus ochrogaster) in northeastern Kansas. Univ. Kansas Publ. Mus. Nat. Hist., 8(6):361-416.

Maslin, T. P.

1959. An annotated check list of the amphibians and reptiles of Colorado. Univ. Colorado Studies, Biol. Series, No. 6, 98 pp.

McCauley, R. H.

1945. The reptiles of Maryland and the District of Columbia. Published by the author, Hagerstown, Maryland, 194 pp.

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