Age structure of passerine migrants at the eastern Baltic coast: the analysis of the "coastal effect"

Abstract

The trapping data of 12 migrant passerine species comprising more than 1,025,000 birds were used to determine age structure of migrants. The data were collected at the Courish Spit of the Baltic Sea during 1972—1995. Six species which are predominantly nocturnal migrants showed the "coastal effect", that is a disproportionately high percentage of immature birds, as opposed to diurnal migrants. The comparison of these results with the data from other studies in the Baltic region incline us to think that the coastal effect is caused by differential behaviour of adults and immatures during landfall after a nocturnal flight over large bodies of water.