The Role of Weather Variables and Flight Direction in Determining the Magnitude of Nocturnal Bird Migration

摘要: Autumn nocturnal bird migration was investigated at two stations in the southeastern United States by means of Weather Surveillance Radar (WSR—57) and visual observations. Multivariate analyses were used to examined influence environmental variables on night—to—night magnitude migration. Landbirds selectively flew with wind, regardless its direction or speed. As a result, they frequently migrated seasonally inappropriate directions. The volume varied several orders from night night, but southward flights averaged about five times larger than those other This implies that birds employed some selection terms weather conditions under which initiated migratory flights. showed wind direction, 24—hr change temperature, an index synoptic situation accounted for 5.2% varaibility passerine Migration also related passage cold fronts. Migations heavier northerly winds, falling temperatures, anticyclonic usually prevails shortly after front. efficiency downwind flight is enhanced facts average winds blow roughly directions show behavioral situations initiate Night—to—night variations density can be basis interactions between circadian nature Zugunruhe, energetic state bird, direct initiation