Nesting Success and Life-History Attributes of Bird Communities Along an Urbanization Gradient
by Joseph A. Reale¹ and Robert B. Blair²
¹ City of Boulder Open Space and Mountain Parks, P.O. Box 791, Boulder, CO 80306
² Department of Fisheries, Wildlife, and Conservation Biology, 200 Hodson Hall, University of Minnesota, St. Paul, MN 55108 (address at time of research: Department of Zoology, Miami University, Oxford, OH 45056)
The increase in urbanization in North America has raised concerns regarding impacts on avian populations. In this study, we measured the nesting success of American robins and northern cardinals and analyzed the changes in bird community along an urbanization gradient in southwestern Ohio. We found that nesting failure was not significantly correlated with the gradient, but that it was correlated to nest height, which decreased significantly from the most natural to the most urban sites. We also found that nesting failure was not predicted by the density of adult birds. At the community level, the number of species that use a multiple-brood breeding strategy increased with urbanization. Furthermore, birds identified as high-nesting species reached their highest proportion at the most natural sites and decreased in number with urbanization. In contrast, low-nesting species exhibited the reverse trend. These findings suggest that nesting success—determined by nest-site availability and the ability to produce multiple broods—may drive the distribution of avian species along an urbanization gradient, and that nesting site is a critical resource that regulates the distribution of birds in urban environments.
Key words: American robin; community; life histories; nesting success; northern cardinal; southwestern Ohio; urbanization