Returning for more prey? Foraging in provisioning male Boreal Owls (Aegolius funereus)

Abstract

Birds providing prey with a clumped distribution often return to the previous capture site after having delivered a prey item at the nest. However, details of this foraging tactic are still poorly known, in particular for birds of prey, which often travel far from their nest. We radio-tracked four provisioning male Boreal Owls (Aegolius funereus) during the nighttime and simultaneously recorded their prey deliveries by a video camera positioned at the nest in an increase year of the vole cycle. The camera allowed prey identification and made it possible to assign prey deliveries to fixes of the foraging owls, i.e. the last recorded fix before the owl returned to the nest for a prey delivery. Within a single night, the owls returned more often than randomly expected to the area where they had captured the previous prey item. A prey item delivered was more likely than randomly expected to be of the same species as the previous prey item delivered. However, the probability of a prey item delivered being of the same species as the previous prey item delivered was independent of whether the owl had returned to the area where it captured the previous prey and did not decrease with longer time elapsed since the previous delivery. The owls did not shift hunting area from one night to the next to a larger extent than they did over a longer time span, and overall tended to shift their hunting area gradually over more nights. Our study should be replicated in a peak vole year with higher prey abundance as well as in a low vole year, which should improve the study results by enabling a higher spatial and temporal resolution of the data on the owls’ movements.