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Damiana Michalonek, Wojciech Busse and Robert Lasecki

Age Structure of the Long-Eared Owl (Asio otus) Migration at Bukowo-Kopań Station (Southern Baltic Coast) in Autumns 1996-2003

Over 2000 Long-eared Owls were caught (217 adult and 1827 immatures) at Bukowo-Kopań station (54°21'N, 16°17'E / 54°28'N, 16°25'E), in the central part of the Polish Baltic coast, during autumn seasons 1996-2003. Migration of this species had wave-like pattern with three distinguished passage waves. There were differences between young and adult birds passage in subsequent passage waves (statistically significant only in autumns 2000 and 2003, in other seasons they were non-significant. The value of X 2-test calculated for all seasons together was high and differences were significant (X 2 = 10.96, p < 0.01). Generally, very high variation must be stressed. Young birds dominated during autumn migration (on average they constituted 89%) but this number varied distinctly in different years. The immatures were the most numerous in the second and third wave (they were especially numerous in the third wave in years with the highest number of caught birds). Adult owls migrated a bit earlier - average passage data was earlier by 1 to 16 days in various seasons. All data point at very high variability of the Long-eared Owl migration and necessity of deeper studies on this phenomenon.

Open access

Damiana Michalonek, Wojciech Busse and Przemysław Busse

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.