Patterns of phenological changes in migratory birds

The phenology of avian migration appears to be changing in response to climate change. Seemingly contradictory diVerences in the timing of these annual cycles have been reported in published studies. We show that diVerences between studies in the choice of songbird species, as well as in the measurements of migration phenology, can explain most of the reported diVerences. 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 speciesí 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 breedingarea residence time (BART). As BART is likely to reXect ecologically important factors, e.g. number of clutches, we expect that only small eVects have been exerted on the breeding ecology of the studied species in the time period investigated.