During the spring seasons of 1967 and 1968 ecological studies were made of nesting Ferruginou.s Hawks (Buteo regalis) in a 325 square mile area in west-central Utah. In the springs of 1967 and 1968 a systematic search was conducted throughout the study area for Ferruginous Hawk nests. When active nests were located they were kept under observation throughout the study. The density of nesting pairs in 1967 and 1968 ranged from 7 to 15.4 square miles per pair. An annual seasonal displacement was exhibited, with Ferruginous Hawks being present in the study area only during the nesting season, which lasted from early March until early September. Nest locations implied a preference to inhabit particular areas. The distance separating neighbors in 1967 and 1968 varied from 2.3 miles to .4 miles. More than ninety percent of the pairs observed attended more than one nest; such supernumerary nests averaged 2.5 per pair. The majority of nests were constructed on the ground. More than half of the nests faced south; only about one-tenth faced north. The typical nest was composed of large sticks, lined with bark , grass, and paper, and had an average diameter of 39 inches, a thickness of 17 inches, a pocket diameter of 14 inches, and a pocket depth of 3 inches. Both members of each pair of hawks were active in nest building, which began in early March. In 1967 thirteen nests produced 20 eggs (1.5 eggs per nest) and 8 young (.67 percent), of which 8 (100 percent) fledged (.67 per nest); in 1968 fourteen nests produced 50 eggs (3.57 eggs per nest) and 33 young (2.36 per nest), of which 28 (85 percent) fledged (2 per nest). Territorial behavior was inconsistent. On occasion each nesting pair was seen to actively defend its territory against other predatory birds; whereas on other occasions intruding raptors met no resistance from the resident pair of Ferruginous Hawks. From 26 eyries, 283 prey individuals were identified. Mammals (92 percent) predominated. The Ord's Kangaroo Rat (Dipodomys ordii) was the most numerous prey species (44 percent), with the Blacktail Jackrabbit (Lepus californicus) being the next most common (30 percent). Birds represented 5 percent of the total prey. Several hunting techniques were exhibited by the hawks. Hunting was usually conducted before sunrise and after sunset each day. Recorded mortality was minimal, with only one dead Ferruginous Hawk observed during the study.



College and Department

Life Sciences; Plant and Wildlife Sciences



Date Submitted


Document Type





Birds, Eggs, Utah; Hawks, Utah; Cedar Valley (Utah County, Utah)



Included in

Ornithology Commons