Influence of wind and geography on orientation behavior of adult Honey Buzzards Pernis apivorus during migration over water

Abstract

During autumn migration across the Central Mediterranean adult Honey Buzzards cross the sea at its narrowest point, between western Sicily (southern Italy) and the Cap Bon Peninsula (Tunisia). This study investigated the influence of prevailing winds and geography on the orientation behaviour of migrants during this sea crossing by observations over two islands, one on the northern side, the other on the southern side of the Channel of Sicily. The flock was taken as the sampling unit. Honey Buzzards reached the island of Marettimo, approx. 30 km off western Sicily and 130 km NE of the Cap Bon Peninsula, regardless of the direction of the prevailing winds (NW and S). By contrast, Honey Buzzards passed via Pantelleria, about 110 km SW of western Sicily and 70 km ESE of the Cap Bon peninsula, mostly during NW winds. Birds readied Pantelleria from the NE and left the island flying WNW. They applied true navigational abilities in choosing the shorter crossing between Pantelleria and Tunisia and showing a curvilinear migration. Our results agree in part with the "optimal use of wind" hypothesis. In particular, wind, geography and navigational abilities seem to interact to shape the orientation behaviour of migrating Honey Buzzards, perhaps to minimize the risks of non-stop powered flight over the water.