Urban divide: predictors of bird communities in forest fragments and the surrounding urban matrix

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ABSTRACT Over 50% of the world’s human population lives in cities, and the rate of urbanisation continues to increase globally. Consequences of urbanisation, such as noise pollution and land use change, impact bird communities and movement dynamics. Furthermore, cities are fragmented and heterogeneous, so it is pertinent to assess how birds respond to urbanisation at different scales. We quantified avian community composition in relation to environmental variables at 1) a city scale across an urbanisation gradient, and 2) a smaller spatial scale, within urban forest fragments. In the gradient study, species richness was highest in the peri-urban zone and declined with urbanisation. Bird density peaked at a moderate level of urbanisation, with medium housing density. Native species were more likely to be recorded where there were more shrubs and trees, less noise pollution and fewer impermeable surfaces. Within urban forest fragments, bird communities were less likely to be dominated by a few introduced species, and had high native species richness relative to counts in the urban matrix. Increased native bird richness and abundance within fragments were primarily associated with less noise and lower neighbouring human density. Differences in bird composition between the urban matrix and urban fragments suggest the matrix can be improved to facilitate the dominance of native bird species by reducing noise and adding vegetation. Understanding how birds use urban environments not only allows us to measure changes as a result of urban intensification but also allows for management of cities to improve the status of urban bird communities.