Park size and prey density limit occurrence of Eurasian Sparrowhawks in urban parks during winter

Claudia Schütz,Christian H Schulze

doi:10.1186/s40657-018-0122-9

Abstract

BackgroundEurasian Sparrowhawks (Accipiter nisus) increasingly represent successful city-dwellers. Thereby, a rich food supply indicated by high numbers of small birds is believed to be the key driver for this bird-eating raptor species to settle in urban environments. However, as small passerine birds show particularly strong antipredator responses, sparrowhawks may not simply focus on patches of highest prey densities, but rather respond strategically to prey behavior, raising the importance of other parameters in determining the occurrence within urban landscapes.MethodsTo deepen our knowledge on habitat requirements of urban sparrowhawks, bird surveys were carried out during winter between December 2005 and January 2017 in 36 city parks in Vienna, Austria. Besides food supply also park size, canopy heterogeneity and the connectivity with other green spaces were considered.ResultsOccurrence of sparrowhawks was positively affected by increasing park size, prey density and the interaction between both. Bird feeder density and park connectivity with other green spaces were of minor importance in explaining the presence of this species. Canopy heterogeneity didn’t affect city park occupancy by Eurasian Sparrowhawks.ConclusionsOur results suggest that large city parks, particularly when characterized by high prey densities, substantially contribute to protect and preserve ecologically important bird species such as raptors within the urban environment—a landscape already struggling with biodiversity losses and functional homogenization.

Highlights

Eurasian Sparrowhawks (Accipiter nisus) increasingly represent successful city-dwellers
Sufficient food supply indicated by high numbers of small birds is believed to be the key resource when settling in urban habitats (Newton 2010)
We investigated if the occurrence of Eurasian Sparrowhawks in city parks follows classical concepts of foraging theory, with predators choosing patches of highest prey densities, or if this small raptor rather responds strategically to prey behavior, raising the importance of other parameters in predicting its occurrence within urban parks (Lima 2002)

Summary

Introduction

Eurasian Sparrowhawks (Accipiter nisus) increasingly represent successful city-dwellers. City parks with a rich food supply may be frequently occupied by sparrowhawks This may be important during winter, when large numbers of small passerines are attracted to bird feeders (Jokimäki and Suhonen 1998). Studies on bird-eating Sharpshinned Hawks (Accipiter striatus) have already shown that hawks maintain spatial and temporal unpredictability in their movements instead of focusing on areas with high prey densities. Their hunting attempts proved more successful when attacking solitary feeding prey than prey foraging in groups (Roth II et al 2006; Roth II and Lima 2007)

Methods

Results

Discussion

Conclusion