Roost occupancy and behaviour at evening departure werestudied in long-eared owls(Asio otus) at a large winter roost in thesouthern suburbs of the city of Milan, northern Italy. The numberof roosting owls was strongly correlated with decreasingdaylength,while it was weakly negatively correlated with temperature. Hence changes in photoperiod can be considered amongthe proximate factors promoting the winter aggregation of long-eared owls. Behaviour at departure was influenced by cloudcover: birds departed earlier, and departures were at a higher altitudeand less concentrated, with covered sky than with clear sky; thereasons for these behavioural differencesremain unclear. Directions of departure showed that owls do not use the urban area forhunting, as no birds were observed flying towards the city, consistently with dietary data.
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