Flight directions and density of nocturnal passerine migration in the northern part of the Balkan peninsula in autumn: preliminary results

摘要

First results of study of flight direction and density of nocturnal passerine migration by the moon-watch method during 22 nights in autumn in NE Bulgaria are presented. Trapping data from August – October 1977, 1979 and 1997 concerning passerine nocturnal migrants at two stopover sites is analysed. In August and September 98-100% of trapped nocturnal migrants are trans-Saharan migrants. The main direction of nocturnal passage of these birds is SSE (165° - 170°) in August and SSE-S (176° - 179°) in September. The seasonal shift of main flight direction of nocturnal migration from SSE-S (August and September) to SSW-SW (October) is caused by differential passage of species with different wintering areas. The average density of nocturnal passerine migration (migration traffic rate) comprised 14 490 birds?night￣1?km￣1 in September and 8080 birds?night￣1?km￣1 in October. On one September night an average of 11 million passerines may cross the whole northern part of the Balkan Peninsula.