foraging of two wintering Buzzards
Birds wintering in the northern Palearctic compensate for substantial energy losses and prepare for a food deficit in winter by suitably modifying their foraging behaviour. Besides weather conditions, interspecific competition is another factor driving hunting strategies. In order to describe this phenomenon, we observed the behaviour 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 perches. Rough-legged Buzzards conspicuously avoided using fence posts for scanning the surroundings and spent the most time perching on the ground. Common Buzzards more often used trees for this purpose when the snow cover was thicker. The thickness of the snow cover was negatively correlated with the number of attempted attacks on prey by both species and caused Common Buzzards to change their perches less frequently. A positive relationship was found between the number of perch changes and the number of attempted attacks. The upshot is that the ultimate effectiveness of hunting is mediated not by the type of perch but by the overview of the foraging area from different heights and perspectives. Snow cover was the most important factor modifying foraging behaviour and possibly intensifying interspecific competition.