Seasonal migration pattern of owls at Bukowo-Kopań station (N Poland) in 2000-2003

Data were collected at the Operation Baltic stations and included over 2000 owls caught and ringed at Bukowo-Kopań station in autumns 2000-2003. Birds were caught with raptor nets, ringed and measured according to the Operation Baltic standards.

The Long-eared Owl (Asio otus) is the most numerous migrant at Polish coast of the Baltic Sea. Migration of this species has wave-like pattern with few nights of very high owl numbers after nights without these birds. Amount of migrants changes decidedly from year to year. This is a result of fluctuations associated with small mammal populations dynamics. Other owl species pass Bukowo-Kopań station in rather low numbers. We can distinguish two groups of owl species according to terms of passage peaks. Both the Short-eared Owl (Asio flammeus) and the Barn Owl (Tyto alba) migrate in the highest numbers generally at the same time as the Long-eared Owl, i.e. at the beginning of November. Correlation is in most cases statistically significant. On the contrary, the migration pattern of the Tengmalm's Owl (Aegolius funereus) is conspicuously different. Passage maximum of this species occurs at the beginning of October and by 25 October the passage is almost finished. But even then individuals that migrate later are caught during the same migration peaks as the Long-eared Owl.

Obtained results indicate that the passage of different owls is similar to the most numerous and typical migrant species - the Long-eared Owl. Other species choose the same nights for passage, which suggests that some common factors influencing owl migration exist.