Bird species assemblages differ, while functional richness is maintained across an urban landscape

Abstract

Urbanization poses serious threats to biodiversity in many regions of the developing world. Understanding the factors that influence bird communities at the local and landscape level is important to guide urban planning efforts toward enhancing bird diversity. How bird species richness and diversity vary and the environmental factors that optimize their functional diversity in urban settlements remains poorly understood. We investigated the relationship between environmental characteristics and bird taxonomic and functional diversity across an urban settlement density gradient in Harare, Zimbabwe. Seventy-two transects were surveyed for bird species and environmental characteristics, and 6639 birds representing 94 species were recorded. Bird species richness and diversity declined from low to high settlement density sites, whereas bird functional diversity and abundance did not vary across the urban settlement density gradient. Characteristic species for low and high settlement density sites were Purple-crested Turaco (Tauraco porphyreolophus) and Pearl-breasted Swallow (Hirundo dimidiata), respectively. There were significant dissimilarities in bird species assemblages across the urban gradient. We demonstrated that the presence of water features and vegetation (presence of flowering plants and tree height) were the most significant environmental predictors of bird functional diversity. Loss in species richness across the urban settlement density gradient does not seem to be accompanied by significant declines in functional richness. The key message for urban planning here is that; despite the homogenization of urban environments and loss of bird species richness (Melles et al., 2003), broad ecosystem functionality may be maintained across the urban settlement density gradient.