Abstract
Birds wintering in the northern Palearctic compensate for substantial energy losses and prepare for a food deficit in winter by adjusting their foraging behavior. Apart from weather conditions, interspecific competition also drives hunting strategies. To describe this phenomenon, we observed the behavior of two sympatrically wintering raptor species: the Common Buzzard and the Rough-legged Buzzard. The study was carried out in east-central Poland during four seasons on a study plot where the densities of both species were high. Interspecific differences were detected in the use of available hunting sites. Rough-legged Buzzards conspicuously avoided using fence posts for scanning the surroundings and spent the most time standing on the ground. Common Buzzards more often used trees for this purpose when the snow cover was thick. Thicker snow cover resulted in fewer attempted attacks on prey in both species and caused Common Buzzards to change their hunting sites less frequently. The study also showed that the more often a bird changed its hunting site, the greater the number of attempted attacks. The outcome is that the ultimate effectiveness of hunting is mediated by the overview of the foraging area from different heights and perspectives, not by the type of hunting site. Snow cover was the most important factor in modifying foraging behavior and possibly intensifying interspecific competition.