Climatic effects on arrival and laying dates in a long-distance migrant, the Collared Flycatcher Ficedula albicollis

Long-distance migrants may respond to climate change in breeding, wintering or staging area by changing their phenology. The geographical variation in such responses (e.g. coastal vs. continental Europe) and the relative importance of climate at different spatial scales remain unclear. Here we analysed variation in first arrival dates (FADs) and laying dates of the Collared Flycatcher Ficedula albicollis in a central European population, from 1973 to 2002. The North Atlantic Oscillation (NAO) index correlated weakly with local temperature during the laying period. Decreasing spring temperatures until 1980 were associated with a trend towards later laying. The rate of warming (0.2 degrees C per year) and laying advancement (0.4 days per year) since 1980 are amongst the highest values reported elsewhere. This long-term trend in laying date was largely explained by the change in climatic factors. The negative effect of local spring temperature on laying was relatively stronger than that of NAO. The number of clutches initiated on a particular day was marginally affected by the temperature 3 days prior to laying and the response of females to daily variation in temperature did not change over years. Correspondence between the average population-level and the individual-level responses of laying date to climate variation suggests that the advancement of laying was due to phenotypic plasticity. Despite warmer springs and advanced laying, FADs did not change over years and were not correlated with local spring temperature. Marginal evidence suggests later departure from wintering grounds and faster migration across staging areas in warmer conditions. Advancement of arrival was probably constrained by low local temperatures in early spring just before arrival that have not changed over years. The interval between first arrival and laying has declined since 1980 (0.5 days per year), but the increasing temperature during that period may have kept the food supply approximately unchanged.