Investigating the influence of local weather conditions and alternative prey composition on the breeding performance of urban Eurasian Kestrels Falco tinnunculus

Abstract

ABSTRACTCapsule: Local weather conditions, but not a city-associated diet composition, influence the breeding performance of urban Eurasian Kestrels Falco tinnunculus.Aims: We aim to explore the impact of diet composition, specifically a high proportion of avian prey, on the breeding performance of urban Eurasian Kestrels under different weather conditions.Methods: The Eurasian Kestrel is known to exploit cities and occurs in the study area of Vienna, Austria (415 km2) at high breeding densities of 89–122 pairs/100 km2. Unlike their rural conspecifics which specialize in voles, urban Kestrels are generalists, preying on passerines and mammals, but also reptiles and insects. We explore this alternative diet through pellet analyses along an urbanization gradient over a 5-year period and link diet to reproductive performance, taking local weather conditions into account.Results: Our results showed that weather had a greater influence on breeding performance than did diet. Warm and dry weather during the arrival and courtship period was correlated with earlier egg-laying, higher nestling survival and an overall higher breeding success. Dry winters increased the proportion of mammalian prey, whereas low temperatures and high rainfall during the nestling phase increased the proportion of avian prey. Overall, a more diverse diet was also associated with higher rainfall, but only during the arrival and courtship period.Conclusion: Our research shows a stronger connection between breeding performance and weather conditions than between breeding performance and diet composition, although there may be indirect effects of weather on prey availability which augment the impact of diet on reproductive output in the Eurasian Kestrel.