秋季迁徙中白头鹞与鹃头蜂鹰的跨海迁飞行为比较

在意大利中部的观察点,我们对秋季向非洲迁徙的白头鹞(Circus aeruginosus)和鹃头蜂鹰(Pernis apivorus)的跨海迁飞行为进行了研究.其中白头鹞大部分为成鸟,鹃头蜂鹰大部分是亚成鸟.研究内容包括跨海迁徙行为与风向、昼间迁徙时间、集群和年龄的关系.尽管鹃头蜂鹰不如白头鹞适合长距离跨海飞行,但它们集群迁徙时多远离海岸.两种鸟中只有很少个体选择沿海岸飞行.在无风天气,白头鹞像单独迁徙的鹃头蜂鹰一样,选择跨海飞行,而不是中途停歇或飞回陆地的断续迁徙,在逆风情况下则相反.而鹃头蜂鹰集群迁徙时的飞行策略不受风向影响.两种鸟在上午均选择跨海飞行而不是断续迁徙,下午则相反.鹃头蜂鹰的跨海迁飞行为与年龄相关,其成鸟很少跨海飞行.本研究证实鹃头蜂鹰迁徙过程中集群行为对其跨海迁飞的影响极为显著.不同年龄鹃头蜂鹰的跨海迁飞倾向不同,缺乏经验的亚成鸟和年轻成鸟选择高能量消耗的长途(跨海)飞行,而不是具中途停歇地的短距离断续迁徙.

Comparison of the water-crossing behavior of Western Marsh Harriers(Circus aeruginosus)and European Honey Buzzards (Pernis apivorus)during autumn migration

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.