Hunting flight behaviour of the Eleonora's Falcon Falco eleonorae

The Eleanora's Falcon Falco eleonorae breeds on islands and islets in the M editerranean region and feeds its young on migratory birds caught in the ai r. The breeding season is scheduled to coincide with the peak of bird migra tion. Between IZ and 70 September 1997 we measured Eight tracks of falcons within a range of 4 km from their breeding cliffs on Isola di San Pictro 6 km off the south-west coast of Sardinia, by using an optical range finder. The male falcons left the colony in directions between VV and NW to hunt fa r 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 fa r off-shore hunting area climbed to altitudes over 1000 m. The highest alti tude recorded was 1649 m. The altitudes reported from radar studies on noct urnal migrants in the Mediterranean match the flight altitudes observed in the departing Eleonora's Falcons. Calculations based on th 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 dri ft caused by cross winds when departing for off-shore hunting. Complete com pensation 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 Eight time of Eleonora's Falcons did not seem to be severely restricted by a metabolic ceiling, although such a ceiling does not allow extensive d ay and night hunting.