Conservation related conflicts in nest-site selection of the Eurasian Kestrel (Falco tinnunculus) and the distribution of its avian prey

Abstract

The urban space is a permanently changing ecosystem, suffering from decreasing biodiversity, but also providing new anthropogenic habitats for some adaptable species. The Eurasian kestrel (Falco tinnunculus) is such an adaptable species, whose dense urban populations are ethologically different from rural populations in Europe. Several studies have indicated that urban kestrels increasingly prey on birds; this study even indicated avian prey as the main prey category in the inner-city habitat. We analyzed the selection of habitat and building structure parameters while controlling for differences in their availability in Vienna, Austria, a city of 1.7 million inhabitants. We then connected the nest-site selection of urban kestrels to their diet choice and annual reproduction rate. Our results indicated a trade-off between higher nest-site availability in the center and longer distances to larger open green space as optimal foraging ground. Between 2010 and 2012, a preference for breeding in close vicinity to green backyards was linked to earlier clutch dates, higher hatching rates and larger fledged brood sizes, but the overall productivity per nest still remained low in the center compared to the suburban area. In a survey of avian prey species, we found comparable abundances of prey-sized bird species in green backyards, parks and surrounding suburban areas. We thus hypothesize that kestrels use the immediate nest-surroundings to hunt, but are not as efficient in hunting avian prey as they are in hunting voles. Changes in modern city architecture and renovation of historical buildings pose conservation related threats to urban predators and prey.