Hawks Take Out Sparrows

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Science  23 Jul 2010:
Vol. 329, Issue 5990, pp. 370
DOI: 10.1126/science.329.5990.370-c

Through its adaptability, deliberate and accidental introductions, and natural dispersal, the house sparrow (Passer domesticus) became the archetypical bird of human-modified habitats around the world. In recent decades, however, populations in many parts of its range have declined markedly. That trend has been attributed to changes in agricultural practices, but in Britain urban populations have suffered the steepest declines. Bell et al. therefore consider the role of predation, specifically by the Eurasian sparrowhawk (Accipiter nisus). Using occurrence data from winter garden feeding stations, the authors compare the eastward and southward recolonization of Britain by the sparrowhawk with spatial and temporal patterns in sparrow populations. A logistic model that incorporates predation successfully simulates the trajectories among sparrow populations in rural and urban sites in different regions. At sites, sparrow numbers were generally stable or increasing before the reestablishment of sparrowhawks; afterward, the numbers declined continuously. In addition, significantly greater declines in sparrow numbers were found where sparrowhawks were present. The authors also suggest that urban sparrows had long been free of pressure from avian predators, which left them especially vulnerable when sparrowhawks colonized urban areas.

Auk 127, 411 (2010).

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