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.
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 inFig. 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 headraised, 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 informationis 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.
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.
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 thatmove 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 separatedon the averageby 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 for132 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 hadmoved 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.
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.
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.
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.
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 suggeststhat, 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, thefrog 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 southernIllinois. 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 (Mustelasp.—presumably the diminutiveM. rixosa—Atkinson, 1901:148); 3 undetermined mammals, 1 rabbit, 1 undetermined mouse, 7 voles (2Microtussp., 4M. pennsylvanicus, 1Clethrionomys 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 (Ceuthophilussp.), 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 (1Liopeltis vernalis, 1Storeria occipitomaculata, 1 undetermined), 6 white-footed mice (1Peromyscus leucopus, 5P. nuttalli), 1 vole (Microtus pennsylvanicus), 16 crickets (9Gryllus pennsylvanicus, 4G. assimilis, 2Miogryllus verticalis, 1Nemobius fasciatus), 2 grasshoppers (Dissosteirasp.), 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 (Peromyscussp.) 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 (Ranasp.) made up 9.38 per cent, 1 fence lizard (Sceloporus undulatus) made up 6.25 per cent, and insects, including cicadas (Tibicensp.) 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 (includingHyla 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) instomachs. 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 fasciatusandE. 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;Ranasp., 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 betweenC. c. priapusandC. c. flaviventris, Cagle (1942:188) examined several stomachs and found 1 chipmunk (Tamias striatus), 2 voles (Microtussp.), 2 mice (Peromyscussp.), 2 green snakes (Opheodryssp.), 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, 73Peromyscussp., 19Microtus ochrogaster, 9M. pinetorum, 12Sylvilagus floridanus, 3Scalopus aquaticus, 3Rattus norvegicus, 4Mus musculus, 2Tamias striatus, 2Synaptomys cooperi, 16Rana pipiens, 8Acris crepitans, 2Rana clamitans, 2R. palustris, 1R. catesbeiana, 4Hyla crucifer, 3Pseudacris nigrita, 4Lampropeltis calligaster, 4Sceloporus undulatus, 4Chrysemys picta, 1Heterodon platyrhinos, 1 unidentified reptile, 4Sturnella magna, 1Otocoris 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 undulatusand perhaps others) in eight, frogs (Rana pipiens) in seven, and birds in three.The food ofC. c. stejnegerianusis 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 (Holbrookiasp.), 40.1; scaly lizards (Sceloporussp.) 2.1; frogs (Ranasp.) 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 ofC. c. mormonis 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, 6Melanoplussp., 3M. mexicanus, 2M. devastator, 1M. bivittatus, 2Dissosteira carolina, 1Chortophaga viridis, 3Neduba carinata, 3Trimerotropussp., 7Hippiscussp., 2Steiroxyssp., 3Canoula pellucida, 2Stenopelmatus fuscus, 2S. pictus, 4Gryllus assimilis, 4Ceuthophilussp., 1Pristoceuthophilus pacificus, 6Gammarotettix bilobatusand 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 (Stenopelmatussp.).Several authors have published specific information regarding the food ofC. 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 (Ranasp.), 31 crickets (Gryllus assimilis), 4 decticines, 2 acridids, grasshoppers (1Hippiscus, 2Melanoplussp., 1M. confusus, 1M. differentialis, 1Dissosteira carolina, 1Sphargemon collare, 1Trimerotropussp., 1Orphulellasp., 1Chloealtis conspersa, 1Chortophaga viridifasciata, 1Omaseussp., 1Pedocetessp.), 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 differentialisand 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 (Reithrodontomyssp.). 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.
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 (Mustelasp.—presumably the diminutiveM. rixosa—Atkinson, 1901:148); 3 undetermined mammals, 1 rabbit, 1 undetermined mouse, 7 voles (2Microtussp., 4M. pennsylvanicus, 1Clethrionomys 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 (Ceuthophilussp.), 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 (1Liopeltis vernalis, 1Storeria occipitomaculata, 1 undetermined), 6 white-footed mice (1Peromyscus leucopus, 5P. nuttalli), 1 vole (Microtus pennsylvanicus), 16 crickets (9Gryllus pennsylvanicus, 4G. assimilis, 2Miogryllus verticalis, 1Nemobius fasciatus), 2 grasshoppers (Dissosteirasp.), 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 (Peromyscussp.) 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 (Ranasp.) made up 9.38 per cent, 1 fence lizard (Sceloporus undulatus) made up 6.25 per cent, and insects, including cicadas (Tibicensp.) 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 (includingHyla 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) instomachs. 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 fasciatusandE. 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;Ranasp., 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 betweenC. c. priapusandC. c. flaviventris, Cagle (1942:188) examined several stomachs and found 1 chipmunk (Tamias striatus), 2 voles (Microtussp.), 2 mice (Peromyscussp.), 2 green snakes (Opheodryssp.), 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, 73Peromyscussp., 19Microtus ochrogaster, 9M. pinetorum, 12Sylvilagus floridanus, 3Scalopus aquaticus, 3Rattus norvegicus, 4Mus musculus, 2Tamias striatus, 2Synaptomys cooperi, 16Rana pipiens, 8Acris crepitans, 2Rana clamitans, 2R. palustris, 1R. catesbeiana, 4Hyla crucifer, 3Pseudacris nigrita, 4Lampropeltis calligaster, 4Sceloporus undulatus, 4Chrysemys picta, 1Heterodon platyrhinos, 1 unidentified reptile, 4Sturnella magna, 1Otocoris 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 undulatusand perhaps others) in eight, frogs (Rana pipiens) in seven, and birds in three.
The food ofC. c. stejnegerianusis 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 (Holbrookiasp.), 40.1; scaly lizards (Sceloporussp.) 2.1; frogs (Ranasp.) 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 ofC. c. mormonis 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, 6Melanoplussp., 3M. mexicanus, 2M. devastator, 1M. bivittatus, 2Dissosteira carolina, 1Chortophaga viridis, 3Neduba carinata, 3Trimerotropussp., 7Hippiscussp., 2Steiroxyssp., 3Canoula pellucida, 2Stenopelmatus fuscus, 2S. pictus, 4Gryllus assimilis, 4Ceuthophilussp., 1Pristoceuthophilus pacificus, 6Gammarotettix bilobatusand 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 (Stenopelmatussp.).
Several authors have published specific information regarding the food ofC. 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 (Ranasp.), 31 crickets (Gryllus assimilis), 4 decticines, 2 acridids, grasshoppers (1Hippiscus, 2Melanoplussp., 1M. confusus, 1M. differentialis, 1Dissosteira carolina, 1Sphargemon collare, 1Trimerotropussp., 1Orphulellasp., 1Chloealtis conspersa, 1Chortophaga viridifasciata, 1Omaseussp., 1Pedocetessp.), 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 differentialisand 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 (Reithrodontomyssp.). 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 (especiallyC. c. constrictorof 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. stejnegerianusis much likeflaviventrisin the trend of its feeding.C. c. mormonis 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.
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.
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 (144Gryllus assimilis, 36Gryllussp., 3 unspecified); 353 locustid grasshoppers (41 unspecified, 73Arphia simplex, 67Melanoplus femur-rubrum, 66M. bivittatus, 39M. differentialis, 17Melanoplussp., 15Dissosteira carolina, 8Chortophaga viridifasciata, 6Syrbula admirabilis, 6Sphargemon equale, 2Melanoplus scudderi, 2Schistocerca obscura, 1S. americana); 94 camel crickets (Ceuthophilussp.), 93 katydids (36Neoconocephalus robustus, 15Orchelimum vulgare, 15O. nigripes, 6Conocephalussp., 4Orchelimumsp., 2Amblycorypha inasteca, 1Neoconocephalussp., 1Daihinia brevipes); 7 cicadas (5Tibicensp., 1T. pruinosa, 1T.lyrica); 45 unidentified insects; 17 beetles (including 1Phyllophaga, 1Calosoma scrutator, and 2 other carabids); 2 noctuid moths (Mocis latipes) and 1 caterpillar; 2 homopterans, 1 bee, 1 ant, 1 spider; 69 voles (59Microtus ochrogaster, 9Microtussp., 1M. pinetorum); 31 white-footed mice (15Peromyscus leucopus, 14Peromyscussp., 1P. maniculatus); 36 miscellaneous small mammals (6Cryptotis parva, 4Sigmodon hispidus, 4Reithrodontomys megalotis, 3Blarina brevicauda, 2 each ofScalopus aquaticus,Sylvilagus floridanus, and 1 unspecified shrew); 50 snakes (16Coluber constrictor, 15Diadophis punctatus, 14Thamnophis sirtalis, 4Elaphe obsoleta, 1Natrix sipedon); 7 lizards (5Eumeces fasciatus, 1E.obsoletus, 1Cnemidophorus sexlineatus); 3 unspecified "reptiles"; 5 birds (none identified to genus); 3 bird eggs, 1 narrow-mouthed toad (Gastrophryne olivacea).
Fig. 14.Diagram showing estimated percentage by weight of various categories of prey in a sample of 1351 items, including all those represented inFig. 13and 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.
Fig. 14.Diagram showing estimated percentage by weight of various categories of prey in a sample of 1351 items, including all those represented inFig. 13and 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.
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.13and14) and from stomachs show somewhat different trends, and neither is entirely representative of the actual feeding. Also, local differences in food sources are important.
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.13and14) 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 relativelylarge 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, 5Melanoplus bivittatus, 3M. differentialis, 1M. femur-rubrumand one each ofChortophaga viridifasciata,Dissosteira carolina, andSphargemon equale); 8 crickets (Gryllussp.), 3 katydids, 3 camel crickets (Ceuthophilussp.), 3 noctuid moths, 1 larva of a moth; 10 voles (Microtus ochrogaster), 6 white-footed mice (5Peromyscus leucopusand 1P. maniculatus), 4 harvest mice (Reithrodontomys megalotis); 1 shrew (Cryptotis parva); 4 snakes (3Thamnophis sirtalis, 1Storeria dekayi); 4 lizards (2Eumeces obsoletus, 1Cnemidophorus sexlineatus, 1Ophisaurus 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," 2Melanoplus bivittatusand one each ofM. femur-rubrum,M. scudderi,M. differentialis, andArphia simplex); 48 crickets (31Gryllus assimilis, 17 unspecified); 14 katydids (11Daihinia brevipes, one each of rhadiphorine, conocephaline andNeoconocephalussp.); 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 (5Peromyscus maniculatus, 2 unspecified), 4 unidentified mammals, 1 vole (Microtus ochrogaster), 1 shrew (Cryptotis parva), 84 lizards (77Cnemidophorus sexlineatus, 6Sceloporus undulatus, 1 unspecified), 6 snakes (4 "natricines," 1Thamnophissp., 1Pituophis melanoleucus), 1 "reptile," 1 "bird," 9 frogs (4 unspecified, 1Rana catesbeiana, 4Rana pipiens, 1Ranasp., 1Pseudacris triseriata).
The items from stomachs were as follows: 21 grasshoppers (5 oedipines, 4 tryxalines, 5Melanoplus bivittatus, 3M. differentialis, 1M. femur-rubrumand one each ofChortophaga viridifasciata,Dissosteira carolina, andSphargemon equale); 8 crickets (Gryllussp.), 3 katydids, 3 camel crickets (Ceuthophilussp.), 3 noctuid moths, 1 larva of a moth; 10 voles (Microtus ochrogaster), 6 white-footed mice (5Peromyscus leucopusand 1P. maniculatus), 4 harvest mice (Reithrodontomys megalotis); 1 shrew (Cryptotis parva); 4 snakes (3Thamnophis sirtalis, 1Storeria dekayi); 4 lizards (2Eumeces obsoletus, 1Cnemidophorus sexlineatus, 1Ophisaurus 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," 2Melanoplus bivittatusand one each ofM. femur-rubrum,M. scudderi,M. differentialis, andArphia simplex); 48 crickets (31Gryllus assimilis, 17 unspecified); 14 katydids (11Daihinia brevipes, one each of rhadiphorine, conocephaline andNeoconocephalussp.); 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 (5Peromyscus maniculatus, 2 unspecified), 4 unidentified mammals, 1 vole (Microtus ochrogaster), 1 shrew (Cryptotis parva), 84 lizards (77Cnemidophorus sexlineatus, 6Sceloporus undulatus, 1 unspecified), 6 snakes (4 "natricines," 1Thamnophissp., 1Pituophis melanoleucus), 1 "reptile," 1 "bird," 9 frogs (4 unspecified, 1Rana catesbeiana, 4Rana pipiens, 1Ranasp., 1Pseudacris 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 (Microtussp.) and white-footed mice (Peromyscussp.). 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.maniculatusespecially 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 undulatusandS. graciosus), earless lizards (mainly or entirelyHolbrookia maculata), racerunners (Cnemidophorus sexlineatus) and skinks (Lygosoma lateraleandEumecessp.).
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 thescales 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 raceris 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 genusMelanoplusshow 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. BothMicrotusandPeromyscusconform to this trend, but the relative numbers ofPeromyscusrise 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 ItemsRecorded From Blue Racers From Kansas,Chiefly From the Reservation and Rockefeller Tract
Table 6. Distribution of Various Common Prey Animalsin a Sample of 625 Among Racers of Different Size Groups
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 inTable 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 genusMelanoplus—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 genusMelanoplusare relatively large and heavily armored, and so are relatively immune to attacks from the smaller snakes. Small soft-bodied orthopterans includingGryllus,CeuthophilusandOrchelimum, 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 thefemale'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 themale 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 constrictorL) 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) statedthat 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 ofC. c. priapuson 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 ofC. c. mormonin 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, andseemingly 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:
SubspeciesconstrictorMay 12, 1930, in Ohio (Conant, 1938:55)SubspeciespriapusMay 8, 1921, in Georgia (Wright and Wright, 1957:135)May 9, 1921, in Georgia (Wright and Wright, 1957:135)SubspeciesflaviventrisMay 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)SubspeciesmormonJune 10, 1927, in Utah (Cottam, 1937:229)July 7, 1938, in California (Cunningham, 1959:17)
Subspeciesconstrictor
May 12, 1930, in Ohio (Conant, 1938:55)
Subspeciespriapus
May 8, 1921, in Georgia (Wright and Wright, 1957:135)
May 9, 1921, in Georgia (Wright and Wright, 1957:135)
Subspeciesflaviventris
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)
Subspeciesmormon
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:
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.