Early Impacts of Residential Development on Wood Thrushes in an Urbanizing Forest

Environmental protection policies sometimes protect forests along an advancing suburban front although many of the forests may be brought into close proximity to residential housing. Research suggests that even when forests are physically preserved, their bird communities are simplified as the surroundings become urbanized. However, little is known of the time required for these changes to appear or of the mechanisms that drive them. We obtained population measures on the Wood Thrush (Hylocichla mustelina), an urban-sensitive woodland species in at least portions of its breeding range, before, during, and after development occurred alongside a large (140 ha) upland deciduous forest in Waterloo, Ontario, and compared these measures with those from rural control sites. From 1998 to 2001, the number of houses within 500 m of the urbanizing forest increased from 24 to 470. We detected no significant differences between the relative abundance of Wood Thrushes in the urbanizing and rural control sites, nor was there any significant difference in levels of nesting success, productivity, and brood parasitism. We did not detect any significant changes in successive nest locations of individual banded birds in response to encroaching development. These results suggest that the anticipated impacts of development on Wood Thrushes, and perhaps other forest birds, in adjacent woodlands may not be immediate but, rather, they may require a number of years to manifest. The high return rate (59 percent) of adult females on the urbanizing site in 2001 suggests pronounced site tenacity that may offset any aversion to nesting near houses.