Roost occupancy and behaviour at evening departure were studied in long‐eared 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 correlated with decreasing daylength, while it was weakly negatively correlated with temperature. Hence changes in photoperiod can be considered among the proximate factors promoting the winter aggregation of long‐eared owls. Behaviour at departure was influenced by cloud cover: birds departed earlier, and departures were at a higher altitude and less concentrated, with covered sky than with clear sky; the reasons for these behavioural differences remain unclear. Directions of departure showed that owls do not use the urban area for hunting, as no birds were observed flying towards the city, consistently with dietary data.