Many investigators have found that crows feed on grubs and caterpillars (Aldous, 1944; Alexander, 1930; Lemaire, 1950; Kalmbach, 1918; Barrows and Schwarz, 1895). A number of county agents with whom I had correspondence mentioned that crows aided the farmer in this way. More investigation is required to determine the significance of crow predation upon insect larvae in this area. Most of the bone material recorded was fragmentary. Phalangeal or podial elements of rodents and various bones of rabbits were identified. The only teeth identified were those of the genus Rattus. Barrows and Schwarz (1895:24-25) found that small bones of mammals may be completely ground up and digested by the crow. Hence the amount of food furnished by mammals, either alive or as carrion, may be higher than my figures indicate.
Bones of birds were found in only one pellet, obtained in early July. However, few pellets were collected in the nesting season.
The eggshell occurring in the pellets probably was indicative of extensive feeding on dumping grounds, and I received no reports of eggs lost to crows on poultry farms. Such damage has been reduced to a minimum since most poultry flocks are well-housed.
The percentage of aquatic animals (fish, crayfish and snail) in the diet increased during the early autumn, as the creeks dried up in eastern Harvey County, but after mid-October declined rapidly, as all the pools were then gone.
Conclusions
The large wintering flocks of crows are important consumers of grain sorghums in south-central Kansas. In the early autumn when the crow population is building up, it damages the sorghum crop before harvest. The damage varies from year to year, being much more keenly felt in dry years when the crop is poor or in years when the crop is late. However, most of the sorghums, which are the principal item of diet of these wintering crows, are waste grain taken from the fields after harvest. Some of this waste grain taken should be counted as a loss because the farmer would normally let his livestock utilize it.
Crows use newly sown oat fields as a major source of food during the late winter and early spring. However, damage to the crop is slight. Corn is not an important crop in this area. The crow population is low at the season when corn is planted, so probably little damage is done at this time. Much of the corn eaten in winter is waste grain. Feeding on wheat is of little economic importance, since most of that taken is waste grain. Feeding on sunflower seeds may be counted as neutral to slightly beneficial. Damage to watermelons, which are extensively grown in the sandhills region, may be important at times. Crow feeding upon other crops is only locally significant.
Although it has food preferences, the crow is euryphagous, and its diet is governed to a large extent by the availability of various types of food in its habitat. Therefore, in its ecologic relationships with many other species, it is a density dependent predator. It reduces the numbers of a certain species when the latter becomes unusually abundant but lessens the mortality pressure against it when the prey population is low. Predators of this type tend to maintain stability in a community in contrast to the violent oscillations often caused by a more stenophagous predator. This study indicates that in south-central Kansas crows help to stabilize the populations of grasshoppers, ground-dwelling beetles both predaceous and non-predaceous, and probably those of other types of insects whose soil dwelling larvae are subject to predation during summer plowing.
Crows also serve as scavengers, feeding on carrion and at dumping grounds, as indicated by the high frequency of eggshell and mammalian bone in the diet. Bird bones were found in an insignificant amount in this study, but extensive collections were not made during the main nesting season.