Adjusting breeding phenology to climate fluctuations can be problematic for migratory birds as they have to account for local environmental conditions on the breeding grounds while migrating from remote wintering areas. Predicting general responses to climate change is not straightforward, because these responses vary between migrant species due to the species-specific ecological drivers of breeding behaviour. Therefore more information is needed on species with different ecological requirements, including data on heritability of migration, factors driving phenological changes and how climate affects selection pressures.
Here, we measure heritability in settlement dates and the effect of local climate at the breeding grounds on settlement dates, reproductive success and selection patterns in a French population of a trans-Saharan migratory insectivorous raptor, the lesser kestrel Falco naumanni, monitored and ringed since 1996.
Heritability of settlement dates was low (0.07 ± 0.03), indicating a weak evolutionary potential. Nevertheless, plasticity in settlement dates in response to temperatures allowed earlier settlement when early spring was warmer than average. Reproductive success and selection patterns were strongly affected by temperature during settlement and chick rearing respectively. Warmer spring decreased selection for earlier settling and warmer early summer increased reproductive success. Interestingly, selection for earlier settling was more intense in cooler springs, contrasting with patterns from passerines lagging behind food peaks.
Altogether, these results suggest a positive effect of warmer temperatures on breeding performances of lesser kestrels most likely because the French population is at the coolest boundary of the species European breeding range.