Breeding Biology of the Great Gray Owl in Southeastern Idaho and Northwestern Wyoming

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Abstract
In this study, I documented the existence of a breeding population of Great Gray Owls (Strix nebulosa) in southeastern Idaho and northwestern Wyoming and recorded aspects of this species'' breeding biology between 1980 and 1983. Thirty-eight pairs were found; 25 fledged young at least once. Fifteen nests were documented; 40% in old stick nests and 60% on tops of broken-top snags. Nests were frequently reused. Mean date of egg laying was 5 May. Onset of egg laying appeared to be delayed during years of higher snow depth. Mean clutch and brood sizes were 3.3 and 3.0, respectively. Seventy-one percent of the nest attempts were successful. Fledged young moved at a constant rate and direction away from the nest before they were able to fly. Northern pocket gophers (Thomomys talpoides) and voles (Microtus spp.) constituted 57.9% and 34.1% frequency of the diet, respectively. Great Gray Owls nesting near clearcuts had higher percentages of pocket gophers in their diet while those nesting near natural meadows had higher percentages of voles.

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