Remote tracking unveils intercontinental movements of nomadic Short-eared Owls (Asio flammeus) with implications for resource tracking by irruptive specialist predators

Abstract

Nomadic species can rely on unpredictable resources making them challenging to understand and, consequently, to conserve. Here, we present knowledge advancement for a nomadic predator, the Short-eared Owl Asio flammeus, by tracking individuals from a wide latitudinal range inclusive of most breeding populations in western Europe (Iceland, Scotland and Spain). Tracked owls showed pronounced plasticity in both inter- and intra-individual behaviour. Distances between sequential breeding areas of individual owls ranged from 41 to 4216 km, with similar low fidelity to areas used at other times of year. Owls spent most (> 60%) of their time occupying home-ranges (including breeding) and least (< 10%) undertaking long-distance movements. The propensity for long-distance movements was least for the most geographically isolated population, Iceland. Annual survival rates of 47% were lower than expected for an owl of comparable body mass with mortality concentrated during long-distance displacements and immediately after breeding. Extensive, nomadic travel to find areas where large broods might be reared may incur carry-over costs that lower survival. Conservation planning and assessment for nomadic species and their habitats must acknowledge the uncertainties associated with nomadism at scales from local to international.