The Condor

Intensive study of certain phases of the habits of the Red-tailed Hawk (Buteo jamaicensis) was made by the writers at the San Joaquin Experimental Range in the foothills of Madera County, California, during 1939, 1940, and the early part of 1941. This wide-ranging, common, and important raptor is well known through such detailed studies as those of McAtee ( 1935)) Bent ( 1937)) and Sumner (1929). The present study was intended to reveal economic importance of the Red-tailed Hawk as reflected by its feeding habits in one particular region. The rather stereotyped behavior observed by us in such habits as choice of nest sites, choice of. prey, territorial perches, and size of territory, should afford significant contrast with observations on this species under other environmental conditions elsewhere. Individual adaptability enables these hawks to take advantage of varying environmental conditions. Because of their ability to cover great distances, there must be continual interchange of individuals between populations of the narrow foothill belt where our study was made and nearby regions such as the San Joaquin Valley, the Coast Ranges, the timber belt of the Sierra Nevada and the arid Great Basin. Banding records show that individuals may travel hundreds of miles (Bond, 1939:56; Lincoln, 1939:360). Observations on general beha.vior were made incidentally as opportunities arose, but it was the primary purpose of our study to determine the effect of predation of the Red-tailed Hawk on rodent populations by gathering feeding records and data regarding the population density of the hawks. This study was made under the direction of Mr. Everett E. Horn of the United States Fish and Wildlife Service as a phase of rodent ecology in foothill range lands. Field work was shared by Fitch and Swenson. Swenson collected most of the prey records from nests and made hundreds of precarious climbs, often at the risk of attack. The identifications of prey in pellet material were made by Daniel F. Tillotson and Howard Twining. The authors wish to express their appreciation to Alden H. Miller, E. Raymond Hall, and other staff members of the Museum of Vertebrate Zoology for the loan of reference material and for help in identifying certain material found in pellets. Credit is due to E. C. Van Dyke and E. G. Linsley of the Department of Entomology, University of California, and to M. Cazier and C. D. Michener for their aid in the identification of insect fragments. Many thanks are due to ‘Charles Sperry of the Fish and Wildlife Service for his invaluable aid in the identification of difficult items.