From early September to early October sorghum was in full head. The crows spent most of their feeding time in plowed fields, stubble fields, or pastures. Much time was spent along creeks where pools, which contained many small fish, were drying. Pellets were common under a small roost. Grasshoppers and beetles were the two staple foods in the diet at this time, as shown by their high frequencies and high percentages in pellets. The high percentage and frequency of wheat corroborates the observation that most of the feeding was being done in wheat fields. The relatively large percentages of fish bones, crayfish, and snail shells can be correlated with the observation that much time was spent by the crows at the pools in creek beds. Many ants were in the pellets. The total percentage of animal materials in the pellets was much higher in this period than in other periods. Plant material had been the highest, percentagewise, during most of the summer, except in the latter part of July. Most studies of food of the crow have shown a higher content of animal material during the summer than does my study. It would seem that much of the food material which did not show up in pellets during the summer was animal material.
Grasshoppers predominated in the diet in early October; some pellets consisted of little other than grasshopper mandibles and leg joints. Wheat is sown in this area from September 10 to October 15, most of it being sown after October 5, the recommended Hessian fly-free date. Most of the grain sorghum is harvested by mid-October. However, the utilization of both of these items was low in October. By October 10 only one pool was left in the creek bed under observation. The amount of fish bones, crayfish, and snail shells in the pellets decreased during this period.
Killing frosts occurred in mid-October. The percentage of grasshoppers in the diet then declined rapidly and later in the autumn declined more slowly. Nevertheless, grasshoppers and beetles remained the predominant animal-food residues into December and frequencies of occurrence remained relatively high.
As autumn progressed and insects became scarcer, plant material made up an ever-larger percentage of the diet. Wheat and sorghum constituted more than one-half of the food residues in this period. However, in December utilization of sorghum by resident crows in eastern Harvey County decreased. Sorghum is not an important crop in this area.
Roosts of Wintering Crows.—The collections of pellets from roosts of wintering crows in western Harvey County and northeastern Reno County differed in having a higher percentage of plant material. Sorghum, corn, and wheat predominated in early autumn, while sorghum, sunflower seed, and corn predominated in the winter. Ants were utilized to a much greater extent in early autumn. For grasshoppers and beetles, frequency of occurrence was high but percentages were low. Most of the standing water in the sand dune country had dried approximately one year before, and the aquatic component of the diet was almost entirely lacking.
The two principal food items taken by crows in the winter of 1953 were grain sorghum and sunflower seed. Censuses in late November and late December, 1953, showed that feeding was mostly in harvested sorghum fields and corn fields, but alfalfa fields, wheat fields, plowed fields, and native pasture were also utilized.
Sorghum and sunflower seeds were also the staple foods during December, 1952. Oats and wheat showed higher percentages than in 1953, perhaps because different foods were available in these two winters or because of differences in locality. The pellets collected in 1952 were from western Harvey County, whereas most of those collected in 1953 were from northeastern Reno County.
The collection taken in February, 1954, showed a large percentage of oats in the diet. Newly sown oat fields were probably a major source of food at that time.
Economic and Ecologic Significance
The chief factors that determine the economic bearing of crows locally are: the yearly diet, the time of year in which each food item is taken, and fluctuation in the population density at different times of year. In the study here reported upon, the yearly diet was computed by averaging the percentages of each item determined for each biweekly period. Of the twenty-one collecting periods shown in the tables, six are overlapping pairs; that is to say, each includes one collection from eastern Harvey County and one from the western part of the study area. The average of these pairs was used in computing the yearly average. The yearly average is therefore based upon eighteen separate samples.