European Starlings and their effect on native cavity-nesting birds

European Starlings (Sturnus vulgaris) were introduced to New York City in 1890 and have since become one of North America's most common species. Starlings are aggressive competitors and commonly usurp cavities of other hole-nesting species. These characters make it a clear choice for a species whose invasion is likely to have significantly affected native cavity-nesting birds. Using Christmas Bird Counts and Breeding Bird Surveys, 1 compared the mean densities of 27 native cavity-nesting species before and after invasion of sites by starlings. Contrary to expectations, only 10 of the species exhibited significant effects potentially attributable to starlings, and only half of these were in part negative. However, in 2 of the 5 species that showed negative effects, evidence for a decline in one analysis was countered by an increase in the other, whereas in 2 others declines were likely due to factors other than starling competition. Only sapsuckers (Sphyrapicus spp.) exhibited declines potentially attributable to starlings that were not countered by other data. Although declines may still occur if starlings continue to increase, the results of this study fail to support the hypothesis that starlings have had a severe impact on populations of native birds. These results highlight the difficulties of predicting the impacts of invasive species. Native hole-nesting birds have thus far apparently held their own against the starling invasion, despite the latter's abundance and aggressive usurpation of often limited cavities.