Changes in habitat use by the Common Buzzard (Buteo buteo L.) during non-breeding season in relation to winter conditions

Common Buzzards (Buteo buteo L.) found in central Europe are partial migrants and the number of birds which winter on the breeding ground depends on atmospheric conditions. The advantages of wintering on breeding grounds are counterbalanced by the risk of unfarorable atmospheric conditions and influence the birds' migration decision. During the periods from October to March (2002/2003-2004/2005), changes in habitat use by the Common Buzzard were studied in the open terrain of the mountain valley (Kotlina Orawsko-Nowotarska, Carpathians, southern Poland). The results were analyzed according to four meteorological periods (autumn, early winter, winter, early spring). Snow cover caused significant differences in types of habitats used by foraging Common Buzzards. During permanent snow cover the extent to which open areas was used decreased from 65% in periods without snow cover to 52% in other periods. At the same time the number of birds foraging in afforestations increased from 28% during periods without snow cover to 42% during periods with snow cover. The extent to which vegetation types was used also changed significantly. During the winter abandoned lands, which probably offer a richer food base, were used more often (56 vs. 23-33% in periods without snow cover). During permanent snow cover birds used higher perches, which presumably enabled them to observe a larger area and made hunting more efficient and compensated for limited access to prey.