Tree Use and Predator Vulnerability of Wintering Passerines

Abstract

Pygmy Owls in winter took a range of small avian and mammalian prey up to a weight of around 40 g. The owls showed a functional response and concentrated on bird prey at high bird densities, whereas diet composition appeared unrelated to rodent abundance. Small and less profitable avian prey were taken disproportionately often, counter to the expectation from models of an energetically optimized diet. A correlation between prey habitat use and relative predation risk suggests a niche specific difference in vulnerability between prey species as an explanation for the preponderance for small prey species in the diet of the Pygmy Owl. Niche differentiation may not only require adaptations for foraging efficiency but also to different predator regimes.