Drivers of avian species richness and community structure in urban courtyard gardens

Increasing global urbanisation has steered research towards understanding biodiversity in urban areas. Old city spaces throughout Europe have a proliferation of urban court gardens, which can create a mosaic of habitat pockets in an urban area. This article examines the patterns and drivers of avian species richness and community structure in 20 gardens of the constituent colleges of the University of Oxford. We conducted morning surveys across 7 weeks in May and June 2017 and used an information-theoretic approach and model averaging to identify important habitat predictors of species richness. We also studied community structure with Sorensen indices and non-metric multi-dimensional analysis. A total of 43 avian species were observed across all sites. Our sites generally differed in their avian assemblages, with greater species turnover than nestedness between sites. Site area was the strongest predictor of site species richness and surrounding habitat composition was the dominant driver of community structure. Thus, the largest gardens were the most species rich, but species composition among gardens differed based on the habitats in which they were embedded. We support using island biogeography theory to understand the avian species assemblages of urban ecosystems and stress the suitability of our study sites for future urban ecosystem research and generating wildlife awareness.