A population and food-habits study of hawks and owls was made in northcentral Oklahoma between May, 1939, and June, 1942. Both trapping and field observation in 1939 indicated an abundance of Barn Owls, Marsh Hawks, Short-eared Owls, and Screech Owls, as well as the presence in smaller numbers of nine other predatory species. Populations of rodents, particularly cotton rats, were similarly high. Pellet analysis indicated that over 66 per cent of the total food items of the predatory birds in 1939 consisted of cotton rats. Following an unusually cold period in late December, 1939, and early January, 1940, both populations of rodents and species of predatory birds whose food had consisted primarily of cotton rats showed a notable decrease or disappeared altogether. The Great Horned Owl, whose food habits are more generalized, and the Cooper's Hawk, which feeds primarily on small birds, were recorded in their usual numbers after the period of unusual cold. In 1941 and the spring of 1942 populations of predatory birds showed a slight increase, and a few cotton rats were again trapped in late June, 1941, the earliest record following January, 1940.
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