Feeding ecology of breeding Long-eared Owls in southwestern Idaho

Abstract

Feeding ecology of Long-eared Owls (Asio otus) was investigated in the Snake River Birds of Prey Area, southwestern Idaho, during the breeding seasons of 1980 and 1981. The owls preyed mainly on five genera of small mammals: Peromyscus, Perognathus, Dipodomys, Microtus, and Reithrodontomys. There was considerable variation in prey composition among sites but not between years. In both years the proportion of Perognathus in the diet increased after the young owls fledged. Compared with other North American studies, Long-eared Owls in the Snake River Birds of Prey Area had a wider feeding niche and preyed more extensively on nonmicrotines. The range of prey sizes in Long-eared Owl diets was similar to that in other areas, with most prey weighing less than 100 g. Interlocality differences in the Long-eared Owl feeding niche probably reflect differences in the composition of small mammal faunas. Long-eared Owls in the Snake River Birds of Prey Area appeared to feed opportunistically on a diversity of available small mammals; prey size, rather than prey type, was the most important factor in food selection.