Patterns of phenological changes in migratory birds
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The phenology of avian migration appears to be changing in response to climate change. Seemingly contradictory differences in the timing of these annual cycles have been reported in published studies. We show that differences between studies in the choice of songbird species, as well as in the measurements of migration phenology, can explain most of the reported differences. Furthermore, while earlier spring arrival is evident across these studies, trends in timing of departure show large variation between species and according to individual timing of migration (early-arriving vs. late-departing individuals). Much of the variation in departure between species could be explained by each species’ migratory status. We present a detailed analysis of migrants recorded at a Danish migration site, and reveal that although shifts in migration timing can be demonstrated for almost all species, these shifts are either most pronounced in the early arriving/late departing individuals or the changes are similar. Thus most individuals do not seem to change their breeding-area residence time (BART). As BART is likely to reflect ecologically important factors, e.g. number of clutches, we expect that only small effects have been exerted on the breeding ecology of the studied species in the time period investigated.
KeywordsBreeding time Migration Climate change Songbirds Population dynamics
We thank all the ringers working on Christiansø during the study period, as well as Christiansø Research Station. Special thanks are extended to Tom S. Romdal for comments on earlier drafts of this manuscript. The Danish National and Nature Agency and The National Environmental Research Institute, Department of Coastal Zone Ecology financed the collection of the data that made this paper possible. A. P. Tøttrup and C. Rahbek acknowledge the Danish National Science Foundation grant J. no. 21-03-0221 for their support of this research.
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