Unusual migratory behaviour in a newly established subpopulation of Whooper Swan (Cygnus cygnus) breeding in the highlands of Poland

Abstract

The migratory behaviour of a subpopulation of Whooper Swans breeding in highlands of southern Poland was studied over a 17-year period, from 1997 to 2013. Birds ringed in their breeding area spent winters and moulting periods in the vicinity of their natal sites, and the mean distance between breeding area and wintering sites was only 149.1 ± 11.7 km. Moreover, 57.0% of all winter re-sightings were obtained within 100 km of the study area. There was an increase in winter site fidelity by individual Whooper Swans over their lifetime (R 2 = 0.09, p = 0.019), reflected by a linear decrease in the distance travelled between two consecutive winters (b = 0.22 ± 0.09). We did not find any association between winter severity and the birds migratory behaviour, neither in the distance travelled nor the location of winter recoveries. The mean distance between the study area and the moulting site was 142.7 ± 34.6 km and c. 66.6% of ring re-sightings during the moulting period were within 100 km of the study area. During autumn many immature birds were observed close to their parents breeding territory and this could help them reunite with parents or siblings from other seasons. The apparent reduction of migratory behaviour compared with representatives of northern populations indicates behavioural plasticity in the Whooper Swan, which may facilitate further southward expansions of the species.