Fig. 14. Diagram showing estimated percentage by weight of various categories of prey in a sample of 1351 items, including all those represented in [Fig. 13] and others from various parts of Kansas. Since the vertebrate items are on the average much bulkier than the insects eaten, vertebrates comprise most of the food, even though insects are eaten in much larger numbers.
Fig. 15. Diagram showing estimated percentages by weight of various categories of prey in a sample of 69 food items squeezed out of stomachs of the blue racers captured at Harvey County Park. Most of the items were vertebrates, and lizards (Cnemidophorus) were especially prominent in the food at this locality. Samples of prey from scats (included in Figs. [13] and [14]) and from stomachs show somewhat different trends, and neither is entirely representative of the actual feeding. Also, local differences in food sources are important.
Over the same period that the sample of scats was collected, a much smaller food sample of 73 prey items was collected by squeezing recently eaten food from the racers' stomachs, or by finding the snakes actually swallowing their prey. These items from stomachs are listed separately because they include relatively more vertebrates than do the items from scats. A grasshopper or cricket eaten by a large racer might have passed undetected, while a relatively large item such as a vole or lizard would have produced a conspicuous bulge in the snake that ate it, and would have excited the curiosity of the investigator. A second difference is that the items from stomachs included several frogs, whereas amphibians were absent from the much larger sample from scats. A third difference is that the many insects found in stomachs were all orthopterans with the exceptions of three noctuid moths and the larva of a moth. Miscellaneous insects, such as beetles, bees and ants recorded from scats were not found in stomachs. Amphibians eaten are digested so completely that no recognizable parts of them are to be found in scats, but remains of the insects previously eaten by amphibians are to be seen in racers' scats. If not recognized as secondary items, such remains might lead to erroneous conclusions regarding the racer's food.
The items from stomachs were as follows: 21 grasshoppers (5 oedipines, 4 tryxalines, 5 Melanoplus bivittatus, 3 M. differentialis, 1 M. femur-rubrum and one each of Chortophaga viridifasciata, Dissosteira carolina, and Sphargemon equale); 8 crickets (Gryllus sp.), 3 katydids, 3 camel crickets (Ceuthophilus sp.), 3 noctuid moths, 1 larva of a moth; 10 voles (Microtus ochrogaster), 6 white-footed mice (5 Peromyscus leucopus and 1 P. maniculatus), 4 harvest mice (Reithrodontomys megalotis); 1 shrew (Cryptotis parva); 4 snakes (3 Thamnophis sirtalis, 1 Storeria dekayi); 4 lizards (2 Eumeces obsoletus, 1 Cnemidophorus sexlineatus, 1 Ophisaurus attenuatus); 4 frogs (Rana pipiens), 1 tree-frog (Hyla versicolor).
Records from the Harvey County, Kansas study area include a series of 69 food items from 55 stomachs (of living snakes) and 210 food items from 113 scats. There is a relatively high proportion of vertebrates, including some frogs, in the stomachs, and with no frogs but more miscellaneous insect material in the scats. But, for the sake of brevity, the two categories of items are combined in the following list: 55 grasshoppers (12 unspecified, 1 "locustid," 31 "oedipines," 7 "tryxalines," 5 "locustines," 2 Melanoplus bivittatus and one each of M. femur-rubrum, M. scudderi, M. differentialis, and Arphia simplex); 48 crickets (31 Gryllus assimilis, 17 unspecified); 14 katydids (11 Daihinia brevipes, one each of rhadiphorine, conocephaline and Neoconocephalus sp.); 9 noctuid moths and 1 moth larva; 26 miscellaneous insects (including 13 "beetles," 1 elaterid, 1 curculionid, 1 lygaeid bug, 1 ant, 1 wasp); 1 spider, 7 mice (5 Peromyscus maniculatus, 2 unspecified), 4 unidentified mammals, 1 vole (Microtus ochrogaster), 1 shrew (Cryptotis parva), 84 lizards (77 Cnemidophorus sexlineatus, 6 Sceloporus undulatus, 1 unspecified), 6 snakes (4 "natricines," 1 Thamnophis sp., 1 Pituophis melanoleucus), 1 "reptile," 1 "bird," 9 frogs (4 unspecified, 1 Rana catesbeiana, 4 Rana pipiens, 1 Rana sp., 1 Pseudacris triseriata).
Throughout the range of the racer small mammals make up an important portion of the food, and the bulk of those eaten are voles (Microtus sp.) and white-footed mice (Peromyscus sp.). The voles being diurnal, and having habitat preferences similar to those of the racer, are especially subject to attack, but only large adult racers are capable of swallowing a full grown vole. Probably most of the voles eaten are immature. Of the white-footed mice, P. maniculatus especially prefers a grassland habitat, and is usually found in situations frequented by the racer. Being mainly nocturnal and crepuscular, it is usually in hiding at times when the racer is prowling, but may be flushed from its nest in a shallow burrow or beneath a sheltering object, and overtaken by the snake. Other mammals that are important in the food are harvest mice and other mice, shrews, and young cottontails. The latter are small enough to be eaten by racers only in the early stages of their life in the nest before weaning. Rats (Rattus, Sigmodon), moles, sciurids, and weasels are less frequent prey, ordinarily too large to be eaten by racers and taken chiefly as defenseless juveniles.
Predation on birds is relatively uncommon, and in most instances it involves the eggs or nestlings, or fledglings still slow and clumsy and incapable of sustained flight, or, occasionally, injured adults. Nests that are vulnerable are chiefly those of ground nesting species, or of kinds that nest near the ground in grass or thickets. Many of the birds recorded have not been identified to species, but those identified have included a variety of small passerines and also domestic chicks.