Homogenisation of birdsong along a natural–urban gradient in Argentina

This is an Accepted Manuscript of an article published by Taylor & Francis in Ethology Ecology & Evolutionon 2011, available online: http://www.tandfonline.com/10.1080/03949370.2011.567299One of the clearest examples of animal adaptation to urban habitats is the variation in their vocalisations driven by anthropogenic noise. A behavioural process that has received less attention in urban habitats is how anthropogenic barriers influence animal spacing behaviour and communication. I addressed the effects of the distribution of bird territories in urban habitats and the pattern of song differentiation over distance among neighbouring birds. I studied natural and suburban populations of the white-crowned sparrow Zonotrichia capensis in Argentina. This songbird dwells in gardens, but is here less abundant and more regularly spaced than in open woodlands. Neighbouring birds in garden suburbs sang songs that were more similar to each other than neighbouring birds in natural habitats. Song differentiation was greater within natural habitats than within suburbs at distance < 400 m. At larger distances differences among habitats were no longer significant. Neighbour songs were more homogeneous where territories were more regularly spaced, considering all habitats or urban ones only. Selection for individual recognition of neighbours through songs and greater male–male interactions could have enhanced acoustic differentiation in natural habitats. Conversely, weak territorial interactions in suburbs with abundant landmarks may have constrained song output, resulting in song homogenisation. This study points to differences in variability that may be more difficult to detect than differences in acoustic properties per se, and suggests that the effects of urbanisation on animal communication can be underestimated if inter-individual variation is not properly addressed.The work in Argentina was supported by Canal Sur Andalucía and the Estación Biológica de Doñana (CSIC).Peer reviewe