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.

在北欧地区越冬的鸟类，通过适当地调整其觅食行为，以补偿冬季大量能量损失并预备食物短缺。除了天气条件之外，种间竞争亦是驱动狩猎策略的另一个关键因素。为了描述这一现象，我们观察了两种共生越冬的猛禽物种：普通隼和粗腿隼。研究在波兰东中部进行，历经四个季节，在一个两种物种密度均高的研究区域内实施。我们发现，两种物种在利用可用栖息地方面存在种间差异。粗腿隼显著避免使用栅栏柱进行环境扫描，并将大部分时间花费在地面栖息上。当积雪较厚时，普通隼更倾向于使用树木进行此类活动。积雪厚度与两种物种对猎物发起攻击的尝试次数呈负相关，并导致普通隼改变栖息地的频率降低。研究发现，栖息地改变的次数与攻击尝试次数之间存在正相关关系。最终结果表明，狩猎的最终效果并非取决于栖息地类型，而是由不同高度和视角对觅食区域的全面观察所中介。积雪覆盖是影响觅食行为的最重要因素，并可能加剧种间竞争。