Does Seasonal Decline in Breeding Performance Differ for an African Raptor across an Urbanization Gradient?

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 urbanization 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-rural habitat gradient. We found no evidence for a direct effect of urbanization 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 urbanization. Thus, higher productivity was found in more urbanized habitats earlier in the season, but towards the end of the breeding season, birds in less urbanized habitats performed better. Our study represents one of the first to examine avian productivity in relation to urbanization in Africa, and also represents one of the first studies to suggest that seasonal declines in productivity may differ according to levels of urbanization. These results have considerable implications for potential changes in phenology or productivity for the regions' avifauna as African urbanization continues.

The movements of a recently urbanized wading bird reveal changes in season timing and length related to resource use

“…Altered seasonal movement patterns related to anthropogenic resource use as we observed in our study has been documented in other studies [14,54,55]. Altered movement behaviors can lead to range restriction [54], reduced migration distance [9,14], or complete abandonment of migratory movements [13,14,55], and altered seasonal timing and length [56,57].…”

Exploring the Influence of Urbanization On Morph Distribution and Morph-Specific Breeding Performance In A Polymorphic African Raptor

“…In this study, we explore this question of how morphs vary with urbanization in the Black Sparrowhawk, a polymorphic raptor that colonized the area of Cape Town, South Africa, in the last two decades. Black Sparrowhawks appear to have adapted well to urban areas, with more than 50 breeding pairs (Martin et al 2014b) within our study area and no obvious negative health effects on their offspring (Suri et al 2017) or their reproductive rates (Rose et al 2017). In South Africa, morph frequencies vary from east to west along a clinal gradient following winter rainfall patterns (Amar et al , 2014 and the intensity of solar radiation (Tate et al 2016b).…”

“…This study focused on the resident population of Black Sparrowhawks on the Cape Peninsula, Western Cape, South Africa. The study area, approximately 595 km 2 in size (Martin et al 2014a), covers various landscapes including heavily urbanized areas (Rose et al 2017, Suri et al 2017. Quantification of the urban gradient for each nest site was based on a circular buffer with a radius of 2000 m assigned to each nest.…”

“…The chosen scale was based on previous work that quantified home-range sizes during the breeding season from adult males fitted with GPS tags ). Urban cover was calculated based on 72 different land-cover classes at a 30-m resolution from the 2013-2014 South African National land-cover dataset provided by the Department of Environmental Affairs (Rose et al 2017). Percentage urban cover (sealed, unproductive areas of land) was derived for each nest buffer using the packages raster (Hijmans and Van Etten 2014), sp (Pebesma 2004) and rgdal (Bivand et al 2014) in R studio (R Core Team 2016).…”

“…Based on these opposite expectations for habitat selection, we further predict that the timing of breeding may be earlier and breeding performance may be higher in any favored habitat. However, because no negative effects on individual health, including blood parasites (Suri et al 2017), or breeding performance (Rose et al 2017) are known in relation to urbanization in this population, we expect morph distribution to be more closely related to foraging behavior than to a potential adaptive function of eumelanin.…”