Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Wildlife and Fisheries Science

First Advisor

Lester D. Flake


raptor, idaho, idaho national laboratory, birds of prey, ecology


Raptors are high trophic-level predators, and thus sensitive to environmental change. I conducted a basic ecological study of raptors using the Idaho National Environmental Laboratory (INEL), in southeastern Idaho, between 1991 and 1993 to assess effects of human activity on the site. Results were compared to previous raptor studies conducted on the INEL from 1974-1976 and in 1982, as well as with studies of rough-legged hawks, long-eared owls, and burrowing owls conducted during the late 1970’s and early 1980’s. Road-side raptor surveys were conducted from January through May in 1992 and 1993. Principle species recorded were rough-legged hawks, red-tailed hawks, ferruginous haws, gold eagles, prairie falcons, and great horned owls. Most raptors were perched on power poles when I observed them. Sit facilities did not appear to affect wintering raptor distribution. A high occurrence of raptors within 10 km of site facilities was probably a result of power pole distribution, as power poles were usually close to facilities. Raptor populations were comparable to those noted during the 1970’s, but lower than raptor number in 1982. I conducted short-eared owl counts during the spring 1992 and 1993. Counts were accomplished by walking 5 transects (2 km long) and counting all owls flushed. There were no owl flushed, however owls were observed during other phases of this study. Ten kilometers of transect is probably insufficient to monitor short-eared owl populations on the INEL. To establish species occurrence and distribution of owls on the INEL, I conducted nocturnal calling surveys. At regular stops along 5 routes, I played owl calls and recorded all responses. Eight species were recorded during these surveys: great horned owl, long-eared owl, short-eared owl, burrowing owl, boreal owl, northern saw-whet owl, western screech owl, and flammulated owl. Most owls were detected in April and May in the juniper forests around the Lemhi foothills and Twin Buttes. I monitored raptor nesting form March through August, concentrating on medium- to large-sized species. Long-eared owls and great horned owls nested in limited numbers during this study. Owl nesting success was comparable to other studies in the Great Basin region. Red-tailed hawks, ferruginous hawks, and Swaison’s hawks were common nesters on the INEL. Red-tailed hawk numbers have increased since the 1970’s, while Swainson’s and ferruginous hawk numbers have remained relatively stable. Reproductive success was comparable to earlier studies. Nest distribution of ferruginous and Swainson’s hawks was fairly random, with some avoidance of human development in the case of ferruginous hawks. Ferruginous hawks, a Category 2 species under consideration to Threated and Endangered Species status, experienced increased nest failure when exposed to increased human activity on site. Red-tailed hawk nests were clustered along the Big Lost River. Food habits comparisons show dietary overlap between Swainson’s hawks, red-tailed hawks, and great horned owls. Ferruginous hawks and long-eared owls had little overlap with other species. Continued monitoring of raptors on the INEL through prey fluctuations would provide insight into relationships between raptors, as well as with their prey base and habitats.

Library of Congress Subject Headings

Idaho National Engineering Laboratory
Birds of prey -- Ecology


Includes bibliographical references (page 118-127)



Number of Pages



South Dakota State University


Copyright © 1994 Richard Wayne Hansen. All rights reserved.