Hunting Flight Behaviour of the Eleonora's Falcon Falco eleonorae

Abstract

The Eleonora's Falcon Falco eleonorae breeds on islands and islets in the Mediterranean region and feeds its young on migratory birds caught in the air. The breeding season is scheduled to coincide with the peak of bird migration. Between 12 and 20 September 1997 we measured flight tracks of falcons within a range of 4 km from their breeding cliffs on Isola di San Pietro 6 km off the south-west coast of Sardinia, by using an optical range finder. The male falcons left the colony in directions between W and NW to hunt far off-shore, probably intersecting migrants departing from mainland Europe in southern France. Flight tracks of falcons leaving for off-shore hunting and falcons searching for prey closer to the colony differed significantly, as revealed by a straightness index. Falcons leaving the colony for the far off-shore hunting area climbed to altitudes over 1000 m. The highest altitude recorded was 1649 m. The altitudes reported from radar studies on nocturnal migrants in the Mediterranean match the flight altitudes observed in the departing Eleonora's Falcons. Calculations based on the times taken for falcons to return with prey to the nest indicate a maximum distance to the hunting area of about 24 km. The falcons compensated partially for wind drift caused by cross winds when departing for off-shore hunting. Complete compensation might not be possible if the wave pattern of the sea is used for orientation, due to movements of the reference system relative the ground. The flight time of Eleonora's Falcons did not seem to be severely restricted by a metabolic ceiling, although such a ceiling does not allow extensive day and night hunting.