Diet and Prey Consumption Rates of Nesting Boreal Owls, Aegolius funereus, in Alaska

Abstract

Dietary composition and prey consumption rates of nesting Boreal Owls, Aegolius funereus, were investigated during 2004–2006 using two methods. Dietary composition was determined during nest visits through examination of 1882 fresh remains containing at least 11 mammalian and 15 avian species. Consumption rates were calculated based on laboratory examination of seven prey detritus bricks following fledging, yielding 1051 items of five different taxa. During 2003–2006, small mammal snap-trapping was conducted in the vicinity of occupied nest boxes, and relative abundance of potential prey items was estimated. A total of 4020 trap-nights yielded 695 small mammal captures of eight species. Consumption rates of nestling owls ranged from 22.0 to 29.7 g of food per day, averaging 24.2 g (SD = 1.8). Comparisons between availability of small mammals (as indicated by snap-trapping) and consumption (as indicated by nest visits and analysis of prey detritus bricks) showed that Boreal Owls are generally preying on mammals proportionate to their occurrence.