Bimodal orientation and the occurrence of temporary reverse bird migration during autumn in south Scandinavia |
| |
Authors: | S Åkesson Lennart Karlsson Göran Walinder Thomas Alerstam |
| |
Institution: | (1) Department of Animal Ecology, Lund University, Ecology Building, S-223 62 Lund, Sweden , SE;(2) Falsterbo Bird Observatory, Fyren, S-239 40 Falsterbo, Sweden, SE |
| |
Abstract: | Extensive ringing data from a coastal site (Falsterbo Bird Observatory) in southwesternmost Sweden were used to investigate
the occurrence of reverse autumn migration among 20 passerine bird species of widely different migration categories. The data
demonstrate that reverse migration is a widespread and regular phenomenon among nocturnal as well as diurnal migrants and
among irruptive migrants, temperate zone migrants, and long-distance migrants destined for tropical winter quarters. The reoriented
movements were directed approximately opposite to the normal migration direction, i.e. between NNW and ENE from the coast
and towards inland. Median distances of reverse movements varied between 9 and 65 km. Some individuals of irruptive and partial
migrants settled to winter in the reverse direction. Bird species with relatively small fat reserves at capture were more
likely to perform reverse migratory movements than species with larger fat deposits. In two species birds performing forward
migration were significantly heavier within 10 days after capture than individuals performing reverse movements. The reoriented
movements probably are of adaptive significance for birds confronted with the sea and pre-disposed to refuelling during migration.
A bimodal orientation mechanism will bring the birds from an area with high competition for food and high predation risk to
more suitable resting and feeding grounds before resuming migration in the forward direction and crossing the barrier.
Received: 11 July 1995/Accepted after revision: 19 November 1995 |
| |
Keywords: | Autumn migration Ecological barriers Orientation Reverse migration Ringing recoveries |
本文献已被 SpringerLink 等数据库收录! |
|