To cross the sea or to follow the coast? Flight directions and behaviour of migrating raptors approaching the Mediterranean Sea in autumn

We studied the flight behaviour of migrating raptors confronted with the Me diterranean sea at an average coast site near Malaga (Spain) in autumn by m eans of a tracking radar. Behavioural reactions to the water barrier were s pecies-specific, but modified by environmental conditions. Honey buzzards P ernis apivorus and black kites Milvus migrans were reluctant to crossing th e water and followed the east-west leading coast; the few honey buzzards cr ossing the sea at the end of the migratory period were probably juveniles. Considerable numbers of harriers Citrus sp., falcons Falco sp. and ospreys Pandion haliaetus crossed the Mediterranean sea. Falcons crossing the sea h ad higher flight altitudes than those following the coast or crossing the b ay. Sea crossings occurred preferably in following winds and also in sidewi nds, whereas no birds were observed to cross the sea in strong opposing win ds. However, tailwind-support only partly explained for different migratory routes. Raptors crossing the sea in flapping-gliding flight increased airs peeds with sidewinds to reduce drift, but, different from theory, they did not decrease airspeed with increasing tailwind-support indicating that they minimised flight time above sea. Time and energy related consequences of d ifferent flight routes are discussed.