Abstract
As human populations have increased globally, so too has the transformation of natural landscapes into more urban areas. Within Africa, population growth rates and urbanisation rates are amongst the highest in the world, but the impacts of these processes on Africa’s wildlife are largely un-explored. In this study, we focus on a recently established population of black sparrowhawks Accipiter melanoleucus in Cape Town, South Africa. Using long-term data (16 years), we investigate the relationship between the timing of breeding and breeding performance along an urban gradient. We found no evidence for a direct effect of urbanisation on either timing of breeding or breeding performance. However we did find some evidence for a differential seasonal decline in breeding performance dependent on the levels of urbanisation. Thus, higher productivity was found in more urbanised habitats earlier in the season, but toward the end of the breeding season, birds in less urbanised habitats performed better. Our study represents one of the first to examine avian productivity in relation to urbanisation in Africa, and also represents one of the first studies to suggest that seasonal declines in productivity may differ according to levels of urbanisation. These results have considerable implications for potential changes in phenology or productivity for the regions’ avifauna as African urbanisation continues.
Highlights
Urbanization is a rapid and global process in which natural environments are transformed into new urban systems (Berry et al, 1998) which are characterized by an increase of unproductive sealed surfaces in highly disturbed fragmented landscapes (McDonnell and Pickett, 1990)
In this study we focus on the black sparrowhawk Accipiter melanoleucus in South Africa, a raptor that colonized the city of Cape Town in the last two decades after expanding its distribution range from the North-East into the South-West of Southern Africa (Amar et al, 2014)
Our study aims to explore how the breeding performance of urban black sparrowhawks varies with urbanization in Cape Town
Summary
Urbanization is a rapid and global process in which natural environments are transformed into new urban systems (Berry et al, 1998) which are characterized by an increase of unproductive sealed surfaces in highly disturbed fragmented landscapes (McDonnell and Pickett, 1990). The resulting decrease of natural habitat forces ecosystems and species to adapt, avoid or tolerate these new conditions (Blair, 1996; Isaksson, 2015). Key processes that contribute to the impact of urbanization on birds include vegetation changes, habitat fragmentation, introduction of exotic species, changes in food abundance and quality, and novel predator assemblages (Chace and Walsh, 2006). An urban gradient characterizes different levels of urban stressors, such as pollution (light, noise, and air), the abundance of novel predators
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