marsh and Montagu’s harriers over land and over water in the

Water surfaces are natural barriers for Accipitri-formes during migration (Kerlinger 1985, 1989). In fact, migrating raptors tend to use soaring and glid-ing flight over land exploiting thermals to minimize energy costs and avoiding long powered flights over water (Kerlinger 1989). Among species breeding in Europe and wintering in Africa, those with broad wings (eagles, buzzards, vultures) concentrate the crossing of the Mediterranean Sea at the Straits of Gibraltar and at the Bosphorus (Cramp and Sim-mons 1980, Finlayson 1992), while rarely undertak