Climate change and fitness components of a migratory bird breeding in the Mediterranean region

The increase in spring temperatures in temperate regions over the last two decades has led to an advancing spring phenology, and most resident birds have responded to it by advancing their onset of breeding. The pied flycatcher (Ficedula hypoleuca) is a long-distance migrant bird with a relatively late onset of breeding with respect to both resident birds and spring phenology in Europe. In the present correlational study, we show that some fitness components of pied flycatchers are suffering from climate change in two of the southernmost European breeding populations. In both montane study areas, temperature during May increased between 1980 and 2000 and an advancement of oak leafing was detected by using the normalized difference vegetation index (NDVI) to assess tree phenology. This might result in an advancement of the peak in availability of caterpillars, the main prey during the nestling stage. Over the past 18 yr, the time of egg laying and clutch size of pied flycatchers were not affected by the increase in spring temperatures in these Mediterranean populations. However, this increase seems to have an adverse effect on the reproductive output of pied flycatchers over the same period. Our data suggest that the mismatch between the timing of peak food supply and nestling demand caused by recent climate change might result in a reduction of parental energy expenditure that is reflected in a reduction of nestling growth and survival of fledged young in our study populations. The data seem to indicate that the breeding season has not shifted and it is the environment that has shifted away from the timing of the pied flycatcher breeding season. Mediterranean pied flycatchers were not able to advance their onset of breeding, probably, because they are constrained by their late arrival date and their restricted high altitude breeding habitat selection near the southern border of their range.