Winter roost occupancy and behaviour at evening departure of urban long-eared owls

Roost occupancy and behaviour at evening departure were studied in long-eas ed owls (Asio otus) at a large winter roost in the southern suburbs of the city of Milan, northern Italy. The number of roosting owls was strongly cor related with decreasing daylength, while it was weakly negatively correlate d with temperature. Hence changes in photoperiod can be considered among th e proximate factors promoting the winter aggregation of long-eared owls. Be haviour at departure was influenced by cloud cover: birds departed earlier, and departures were at a higher altitude and less concentrated, with cover ed sky than with clear sky; the reasons for these behavioural differences r emain unclear. Directions of departure showed that owls do not use the urba n area for hunting, as no birds were observed flying towards the city, cons istently with dietary data.