Functional and spatial differentiation of urban bird assemblages at the landscape scale

Abstract

We studied the diversity and distribution of diurnal birds in a large city in south-eastern Australia. Approximately 220,000 bird records were extracted from the Atlas of Australian Birds project (1998–2002) for Melbourne, and filtered on the basis of representativeness in surveys. The filtered data for 142 species were subjected to cluster analysis to recognise assemblages, and ordination and guild analysis to determine spatial and functional organisation. Measures of the intensity of urbanisation and environmental characteristics of Melbourne were used to test the separation of the avifauna into broad urban tolerant and urban avoider assemblages and subassemblages. Distribution and relative abundance of urban tolerant birds were found to be positively associated with areas of higher urban intensity, while urban avoiders were associated with areas of lower urban intensity in natural areas within the urban matrix or along its periphery. Urban tolerant species are medium-sized, generalist foragers, which use cavities and canopy sites for nesting, while urban avoiders are either small or very large, foraging specialists (particularly insectivores), which nest on or near the ground as well as in the canopy or shrub layer. Our study confirms that cities do include habitats that are important for a number of urban adapted birds, and suggests ways in which conserving bird diversity can be accommodated in urban planning frameworks.