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Brigham Young University Science Bulletin, Biological Series

Abstract

A comparative study of the breeding ecology of 12 raptor species was conducted in the eastern Great Basin from 1967-1970. The project was designed to determine the composition and densities, habitat selection, territoriality and predatory habits of raptorial birds in a semiarid environment. All topics were analyzed comparatively, relating the requirements and activities of the 12 raptor species.

Average yearly population densities of all species approximated 0.5 pairs per square mile, but much of the available habitat was not utilized. Predominant raptors were the Ferruginous Hawk and Great Horned Owl. Other important raptors included the Golden Eagle, Red-tailed Hawk and Raven.

The breeding activities of the collective raptor populations occurred over a period of eight months. Great Horned Owls and Golden Eagles were the first raptors to initiate nesting activities, usually in late January and early February. The raptor breeding season terminated with the fledging of the young Cooper's Hawks and Burrowing Owls in late August.

The fecundity of the raptor populations varied between years. Specific causes of mortality of eggs and young included nest desertion and destruction, predation, apparent egg infertility, and accidents, most of which could be directly attributed to some form of human interference.

The observed home ranges of the raptor species were a function of their body size and breeding status.

The food of the raptors included at least 55 different prey species, but most relied heavily on only one or two species. A correlation between raptor size and mean prey weight was evident. No examples of raptor predation on game or domestic livestock were found.

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