Timing of autumn migration in Bluethroats Luscinia s. svecica depends on timing of breeding

Abstract

In order to test the hypothesis that interannual variations in the timing of breeding can affect the more precise timing of the autumn migration, the northern Red-spotted Bluethroat was investigated. There was a significant correlation between the timing of breeding at Ammarnäs in Swedish Lapland (median date on the first egg laid) and the timing of the autumn migration in eastern Sweden (median arrival dates to stop-over sites) . This seems to be a causal relationship and suggests that Bluethroats start their autumn migration as soon as possible after breeding and the moult. The evolutionary significance of an early migration start in this species may, for example, be that it is advantageous to reach suitable stop-over sites as soon as possible . A clear relationship between the timing of breeding and migration in Bluethroats implies that the onset of migration is not just a consequence of inherited factors and exogeneous influences, but is also affected by annual phase variations in basic events like breeding. However, breeding itself is not to be considered an independent variable since its timing is possibly influenced by both inherited and exogeneous factors.