Grassland to urban forest in 150 years: Avifaunal response in an African metropolis

Abstract

Avian communities in urban environments of continental Africa are generally poorly understood. Gauteng, one of South Africa's nine provinces and the second largest mega-urban region in sub-Saharan Africa, includes the conurbation of Johannesburg and Pretoria. Rapid urbanisation in the province began in the 1880s after the discovery of gold and is, by northern hemisphere standards, a recent urbanisation event; extrapolating patterns of urban ecology from Europe and North America may therefore not be entirely appropriate. The urban transformation and establishment of an anthropogenically modified to natural vegetation gradient, the extension of woodiness (through bush encroachment and fire exclusion) from the savanna biome into grassland, and the 'greening' of suburbia with an increase in exotic trees and open water, have resulted in a transformed bird community. This tolerant subset of the local avifauna (both native and alien species), derived from species losses (e.g. grassland-specific species) and gains (species responding to more wooded habitats, e.g. dominated by cavity nesters, frugivores, obligate waterassociated species, and cliff nesters), is remarkably diverse and is probably driven and supported by an increase in habitat heterogeneity. An assessment of the bird community at fine- to broad-scale highlights (1) the modifying effect of anthropogenic transformation and the establishment of an urban-resilient bird community brought about by this change, (2) the value of landscape heterogeneity (species composition and structural diversity) in supporting a species-rich bird community, and (3) the value of urban and suburban green spaces as refugia for avian species impacted by urban transformation.