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.