TO CROSS THE SEA OR TO FOLLOW THE COAST? FLIGHT DIRECTIONS AND BEHAVIOUR OF MIGRATING RAPTORS APPROACHING THE MEDITERRANEAN SEA IN AUTUMN

Abstract

Summary We studied the flight behaviour of migrating raptors confronted with the Mediterranean sea at an average coast site near Malaga (Spain) in autumn by means of a tracking radar. Behavioural reactions to the water barrier were species-specific, but modified by environmental conditions. Honey buzzards Pernis apivorus and black kites Milvus migrans were reluctant to crossing the water and followed the east-west leading coast; the few honey buzzards crossing the sea at the end of the migratory period were probably juveniles. Considerable numbers of harriers Circus sp., falcons Falco sp. and ospreys Pandion haliaetus crossed the Mediterranean sea. Falcons crossing the sea had higher flight altitudes than those following the coast or crossing the bay. Sea crossings occurred preferably in following winds and also in sidewinds, whereas no birds were observed to cross the sea in strong opposing winds. However, tailwind-support only partly explained for different migratory routes. Raptors crossing the sea in flapping-gliding flight increased airspeeds 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 different flight routes are discussed.