Climate change and timing of avian breeding and migration throughout Europe

Bird breeding and spring migration phenology have advanced in response to climate change, but the effects differ between sites. Here, we examine the geographical variation in laying-date trends in a short-distance migrant, the European starling Sturnus vulgaris, and a long-distance migrant, the pied flycatcher Ficedula hypoleuca. We model the trend in laying date for these 2 species -between 1980 and 2004 for most of their European breeding areas -by combining geographical variation in mean laying date, the effect of temperature on laying date, and spatial variation in temperature change. Starlings are predicted to have advanced breeding over most of their range, with the greatest advance in north-eastern Europe. In contrast, pied flycatchers have delayed their laying in northern Europe, but have advanced their laying in western and central Europe. The species differ because pied flycatchers lay their eggs 25 d later at each site than starlings, and temperatures during these 2 periods show different trends. Temperatures during migration have also changed differently for populations heading to different breeding areas. This was most pronounced for pied flycatchers; northern populations experience an increase in temperatures during migration, while more southern populations presently still migrate at temperatures similar to those experienced 25 yr ago. As a consequence the southern population may be constrained in adapting to climate change by low temperatures during migration. There is a large contrast in how circumstances during migration and at the breeding grounds have changed: populations that advanced breeding most were subjected to the lowest temperature increases during migration. The temporal and spatial variation in temperature change has important consequences on how migrants adapt to ongoing climate change.