Diets of nesting Boreal Owls, Aegolius funereus, in western interior Alaska

Abstract

Boreal Owls, Aegolius funereus, a circumboreal species, are relatively common throughout interior Alaska where suitable habitat exists. Although research has been conducted on the conspecific Tengmalm's Owl in Eurasia, little is known concerning their requirements in North America, especially in Alaska. Along with other aspects of Boreal Owl ecology, I investigated prey selection and predation rates using nest boxes in western interior Alaska during springs of 1995-1997 based on a total of 778 prey items found in nest boxes. As with studies elsewhere, microtines were the most important dietary component. I hypothesize that plant phenology would influence prey selection during the nesting season because of variations noted in proportions of Northern Red-backed Voles, Clethrionomys rutilus, a forest-dwelling species, and Meadow Voles, Microtus pennsylvanicus, generally preferring more open areas. From the differences noted in proportions of these two species in the diet, I suspect that Meadow Voles are selected for when grasses and sedges are short. When vegetation growth obscures this prey item, Boreal Owls apparently switch to a higher proportion of Northern Red-backed Voles.