The role of habitat variability and interactions around nesting cavities in shaping urban bird communities

Abstract

Aim: To examine how gradients of disturbance (invasion and urbanization) change bird community composition. Location: Eastern Australia Methods: We surveyed avian communities along gradients of invasion at landscape scales (long invaded vs. recently invaded areas) and along local gradients of urbanization (edge, open parks, and urban sub-environments) in New South Wales (NSW) and Queensland (QLD), Australia. Species richness and abundance was calculated for urban sub-environments, and for long and recently invaded areas. We also examined species presence across all sites for each region to evaluate more generally whether individual species were urban exploiters, adapters or avoiders. Results: In total, across nine sites, and 27 sub-environments, we surveyed 127 species in NSW and 144 species in QLD. Most species are urban adapters making some use of some or all urban sub-environments (NSW 83, QLD 84). Edge sites had the highest number of species that did not occur in either urban or park sites (urban avoiders: NSW 23, QLD 31). The lowest richness was found in the most urban sites (urban exploiters; NSW 10, QLD 15). We found that more urban sub-environments contained fewer species, while abundance did not differ. We found little influence of invasive species in shaping urban bird communities. Across urban environments, we found that the presence of an aggressive native species and habitat structure influenced species richness within cities significantly (negative and positive relationships respectively). Main conclusions: Vegetation structure in urban habitats was found to be important for many species, even in the presence of aggressive despotic and invasive alien species. Increasing vegetation structure provides more hiding spaces for small birds in the face of abundant aggressive urban-adapted species. The majority of birds in our surveys are urban adapters such that urban conservation efforts have the opportunity to benefit diverse bird communities.