The Diet of the Eastern Screech-Owl, Megascops asio, at the Northern Periphery of its Range

Abstract

Four techniques: pellet analysis, post-fledging nest inspection, video monitoring, and direct observation were used to study the diet of Eastern Screech-Owl (Megascops asio) in Winnipeg, Manitoba, at the northern limit of the species' range. In 2004 - 2007, 2323 prey items were analyzed. Invertebrates comprised 67% of prey captures but only 11% of biomass consumed. Seasonal shifts in diet between biologically significant periods were significant such that multiple discriminant analyses correctly classified 60% of pre-breeding season, 91% of incubation, 67% of brooding, 86% post-fledging and 100% of winter consumption. Rural pairs consumed a higher percentage of invertebrates and fewer vertebrates than suburban pairs. Prey diversity and niche breadth peaked in low-density suburban areas but rural areas and high-density suburbs were similar in terms of niche breadth. Only 37 vertebrate prey species were recorded and the total niche breadth was 6.5, reflective of a higher degree of diet specialization than more southerly populations.