Biometry of young White Wagtails (Motacilla alba) and Yellow Wagtails (Motacilla flava) caught in the Gulf of Gdansk region during autumn migration

Abstract

Biometry of young White Wagtails ([Motacilla alba]) and Yellow Wagtails ([Motacilla flava]) caught in the Gulf of Gdansk region during autumn migration

Biometrics of juvenile 760 White Wagtails and 714 Yellow Wagtails migrating through the Gulf of Gdansk region in autumn were studied between 1990 and 2000. In both species distributions of wing length, body mass and indices of wing shape were unimodal, with only one exception - in the White Wagtail the wing length distribution showed two peaks caused by sexual dimorphism. The mean body mass and reserves of fat in both species were low in comparison to other stopover sites. There were significant differences in mean weight between birds caught in the morning and in the evening. The majority of birds behave as energy minimising migrants and migrate with low fat reserves in small steps.