Geographical Ecology of the Common Species of Buteo and Parabuteo Wintering in North America

Abstract

North American hawks of the subfamily Buteoninae have received considerable attention, mostly with regard to their food habits and breeding biologies (e.g., Errington and Breckenridge 1938, Fitch et al. 1946, Smith and Murphy 1973). Twelve species occur in the New World north of Mexico but only five are widely distributed in winter (A.O.U. 1957). These are the Harris' Hawk (Parabuteo unicinctus), Ferruginous Hawk (Buteo regalis), Red-shouldered Hawk (B. lineatus), Red-tailed Hawk (B. jamaicensis), and Rough-legged Hawk (B. lagopus). Previously published maps based upon Christmas count data indicate that only the last three of these species are at all common over wide areas (Bystrak 1974). A number of workers have examined the relationships between locally sympatric populations of two or more Buteo species (e.g., Stewart 1949, Orians and Kuhlman 1956, Weller 1964, Schnell 1968). In this study we have compiled data from the 1969-70, 197071, and 1971-72 Christmas counts to determine the overall abundance pattern of this genus in the United States and southern Canada. We could then quantify the contributions made by the individual species to that pattern on different parts of the continent. We compared these calculations with certain environmental variables. Results show the degree to which the species' abundance patterns are complementary, and reveal something about the environmental gradients involved.