Flexibility in spring arrival of migratory birds at northern latitudes under rapid temperature changes

Capsule Icelandic migrants have responded to rapidly increasing spring temperatures on the breeding grounds in recent years. Aims To determine how migrants respond to highly variable spring conditions in their northern breeding areas when they have to cross a barrier on migration. Methods First arrival dates of common Icelandic migrants between 1988 and 2009 were analysed in the light of climate conditions in the breeding and wintering areas. Results Most of the 17 species studied showed a tendency to arrive earlier. Six of the 17 species arrived significantly earlier after milder winters and nine arrived significantly earlier in warmer Icelandic springs. Species wintering further south than northern France showed no timing response to spring conditions in Iceland. Conclusions Migratory birds can respond to high inter-annual variation in spring conditions on the breeding grounds even though they have to face a long journey over a migration barrier. Species that are wintering closer to the breeding grounds or migrating shorter distances in the last leg of the journey seem to be better informed about spring conditions in Iceland and show a more pronounced response to local temperatures.