Consequences of urbanizing landscapes to reproductive performance of birds in remnant forests

Abstract

In contrast to the well-documented changes in avian community structure in urbanizing areas, the demographic consequences of urbanization remain less understood. As such, we examined the extent to which an urbanizing landscape matrix affected avian reproductive performance in forests. From 2001 to 2011, we studied five songbird species in 19 forested sites in Ohio, USA and monitored 4264 natural nests to determine rates of daily nest survival and brood parasitism by brown-headed cowbirds (Molothrus ater). We also tracked the annual number of fledglings produced by color-banded pairs of two focal species, the synanthropic northern cardinal (Cardinalis cardinalis, n=974 breeding pairs between 2003 and 2011) and the urban-avoiding Acadian flycatcher (Empidonax virescens, n=350 breeding pairs between 2001 and 2011). Over the 10-year period, neither daily nest survival nor brood parasitism rates in remnant forests were consistently related to the amount of urbanization in the surrounding landscape matrix for focal species, with the sole exception of Acadian flycatcher for which the percentage of nests with brood parasitism increased with urbanization. Annual reproductive output of cardinals was comparable across the rural–urban gradient, but Acadian flycatchers produced fewer fledglings as urbanization increased. These findings demonstrate that urban-associated patterns of annual reproduction cannot necessarily be inferred from nest survival data alone. Moreover, we show that avian community changes are not the simple consequence of nest predation. Understanding ecological processes that operate within metropolitan areas is critical if we are to conserve biological diversity on our urbanizing planet.