We investigated the water-crossing behavior of Western Marsh Harriers(Circus aeruginosus),mostly adults,and European Honey Buzzards(Pernis apivorus),mostly juveniles,in relation to wind conditions,time of the day,floc...We investigated the water-crossing behavior of Western Marsh Harriers(Circus aeruginosus),mostly adults,and European Honey Buzzards(Pernis apivorus),mostly juveniles,in relation to wind conditions,time of the day,flocking and age classes,at a watchsite in central Italy during the autumn migration en route to Africa.Although European Honey Buzzards are less suited than Western Marsh Harriers to undertake long sea crossings,they were more inclined to leave the coast when migrating in flocks.Few birds of both species chose to fly along the coast.Western Marsh Harriers,such as European Honey Buzzards migrating alone,undertook the water crossing rather than stopping migration(birds roosting at the site or flying back inland) during the absence of wind and vice versa during head winds.Conversely,European Honey Buzzards migrating in flocks were not affected in their decision(crossing or stopping migration) by wind direction.Both species undertook the water crossing rather than stopping migration during mornings and vice versa during afternoons.Finally,in both species,adults and juveniles showed the same behavior in front of a water barrier.This result was expected in the case of the Western Marsh Harrier but not from the European Honey Buzzard since,in this species,the water-crossing tendency is age dependent with adults avoiding sea crossings.Our study confirms that flocking significantly affects the water-crossing behavior of European Honey Buzzards during migration.Moreover,in this species,inexperience of juveniles and presumably younger adults,about the high energetic costs of long powered flight and about the existence of shorter routes over water,might explain the strong water-crossing tendency shown by migrants independently from their age.展开更多
文摘We investigated the water-crossing behavior of Western Marsh Harriers(Circus aeruginosus),mostly adults,and European Honey Buzzards(Pernis apivorus),mostly juveniles,in relation to wind conditions,time of the day,flocking and age classes,at a watchsite in central Italy during the autumn migration en route to Africa.Although European Honey Buzzards are less suited than Western Marsh Harriers to undertake long sea crossings,they were more inclined to leave the coast when migrating in flocks.Few birds of both species chose to fly along the coast.Western Marsh Harriers,such as European Honey Buzzards migrating alone,undertook the water crossing rather than stopping migration(birds roosting at the site or flying back inland) during the absence of wind and vice versa during head winds.Conversely,European Honey Buzzards migrating in flocks were not affected in their decision(crossing or stopping migration) by wind direction.Both species undertook the water crossing rather than stopping migration during mornings and vice versa during afternoons.Finally,in both species,adults and juveniles showed the same behavior in front of a water barrier.This result was expected in the case of the Western Marsh Harrier but not from the European Honey Buzzard since,in this species,the water-crossing tendency is age dependent with adults avoiding sea crossings.Our study confirms that flocking significantly affects the water-crossing behavior of European Honey Buzzards during migration.Moreover,in this species,inexperience of juveniles and presumably younger adults,about the high energetic costs of long powered flight and about the existence of shorter routes over water,might explain the strong water-crossing tendency shown by migrants independently from their age.
