The orientation behaviour of chaffinches, fringilla coelebs, caught during active migratory flight, in relation to the sun.

Abstract

The few orientation studies that have been carried out with day-migrating birds show that they are able to use solar and magnetic orientation cues for orientation. Previous orientation experiments in Emlen funnels have been carried out either with hand-raised birds or with birds caught during resting periods at stop-over sites. The aim of our study was to test whether birds caught during active flight show a higher concentration of migratory activity in the seasonally appropriate migratory direction in the funnels than birds that had not experienced migration just before the funnel experiments. The topography at the alpine pass Col de Bretolet at the border of Switzerland and France allowed us to capture birds during active migratory flight. These birds were in full migration disposition. Orientation experiments with chaffinches suggested an influence of the sun because chaffinches did not orient in the seasonally expected direction, but probably showed positive phototaxis towards the light of the sun at the opposite side of the funnel. Chaffinches tested under overcast conditions oriented to the north-west which probably was a 'nonsense' orientation and not a reverse migration or compensatory behaviour. We conclude that freshly caught birds are too stressed to show appropriate orientation when tested immediately after catching.