Te Arai Kete

Avian productivity in urban landscapes: a review and meta-analysis

D. E. CHAMBERLAIN,1* A. R. CANNON,2† M. P. TOM S,1D. I. LEECH,1B. J. HATCHWELL2& K. J. GASTON2

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Abstract : There is an urgent need to thoroughly review and comprehend the effects of urbanization
on wildlife in order to understand both the ecological implications of increasing urbanization
and how to mitigate its threat to biodiversity globally. We examined patterns in comparative
productivity of urban and non-urban passerine birds, using published estimates from paired
comparisons, and by reviewing and developing explanations in terms of resources, competitors,
predators and other specifically urban environmental factors. The most consistent patterns
were for earlier lay dates, lower clutch size, lower nestling weight and lower productivity
per nesting attempt in urban landscapes; these were supported by a formal meta-analysis.
Nest failure rates did not show consistent patterns across the species considered. We suggest
that food availability is a key driver of differences in passerine demography between
landscapes. In urban habitats, human-provided food may improve adult condition over winter,
leading to earlier lay dates and, in some species, to higher survival and higher breeding
densities, but paucity of natural food may lead to lower productivity per nesting attempt.
We demonstrate that additional comparative research is needed on a wider range of species,
on the effects of natural and human-provided food availability, and on the differences in
survival and dispersal between urban and non-urban populations. Importantly, better-targeted
research and monitoring is needed in areas that are at greatest threat from urbanization,
especially in the developing world.
Keywords:bird food, clutch size, predation, survival, urbanization.