COASTAL MIGRATION AND WIND DRIFT COMPENSATION IN NOCTURNAL PASSERINE MIGRANTS

The orientation of nocturnal passerine migrants in relation to winds a nd coastlines was studied by visual observations (ceilometer observati ons). Numbers and track directions of migrating birds passing at low a ltitude (<200 m) through a vertical light beam were recorded simultane ously at sites along two coastlines at opposite sides of the Falsterbo peninsula in southwestern Sweden in the autumn of 1989. The direction s of the coastlines differed by 34-degrees at the two observation site s, which were only 350 m apart. Observations were made during the firs t part of the night a few hours after sunset. Wind direction and speed were measured at 11 m altitude and the headings of individual birds w ere calculated. The observed mean track direction of the migrants diff ered significantly between the two sites, and coincided with the orien tation of the coastline at each site. At site 1 partial compensation f or wind drift was observed, while at site 2 wind compensation was comp lete. The results show that nocturnal passerine migrants flying at low altitude follow coastlines and that they may use the coastline to com pensate for wind drift. It remains to be shown how wide-spread coastal migration and the use of topographical landmarks are for wind drift c ompensation among nocturnal migrants.