The decline of House Sparrow (Passer domesticus) populations in eastern North America has been proposed to be a consequence of competition between the House Sparrow and the House Finch (Carpodacus mexicanus), both introduced species. Previous research testing the hypothesis that House Sparrow declines are due to competition with House Finches focused on populations in the northeastern U.S., excluding other regions where the species coexist. We tested for effects of competition between these two species in the southeastern U.S. at two scales of analysis. First, we looked for evidence of competition at a local scale during the breeding season by examining patterns of co-occurrence of House Finches and House Sparrows at count points within a 28.3-km2 study area centered on Auburn, Alabama. Second, we tested for the effects of competition at a regional scale across seven southeastern states by analyzing trends in Christmas Bird Count data. Using null-model analysis, we found no evidence for competitive exclusion in our assessment of local co-occurrence, suggesting that if there is competition between these species it is not important enough to affect their spatial distribution during the breeding season. At the regional scale, contrary to findings in the northeastern U.S., the decline of House Sparrow populations within the southeastern U.S. was not significantly correlated with House Finch abundance. Our results suggest that competition with House Finches is not a major cause of decline of the House Sparrow population in the southeastern U.S.
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Vol. 113 • No. 2