Urbanization effects on local birds

While the economic recession of 2008 resulted in a significant slowdown in new housing developments in southwestern North Carolina, it presented a unique research opportunity for LTER researchers Camille Beasley and Dr. Jeff Hepinstall-Cymerman of the University of Georgia to study birds and urbanization in the region.

By looking at “suspended developments,” Beasley and Hepinstall-Cymerman are advancing our understanding of avian responses to urbanization. Put simply, suspended developments are areas where housing construction was halted before any or most houses were built, often because a developer went bankrupt, but in which land was already cleared in preparation for the new neighborhood. These places offer the opportunity to study the direct effects that construction has on bird population without the effect of human influences that accompany studies in regular housing developments.

A suspended development usually consists of some mixture of cleared house lots, roads, electric service, signs, and other basic infrastructure that is installed before houses are built. These features mimic a regular neighborhood, but because humans are not present, the influence of landscaping, domestic pets, and bird feeding is eliminated. This allows researchers to isolate the effects of land use change on bird populations when compared with forested areas and fully developed areas.

Using point counts, where two researchers independently counted and recorded the birds seen and heard at a particular location, Beasley and colleagues collected information about bird populations over two years at 25 sites throughout Macon County and the surrounding area.

By combining information from suspended developments with that from nearby forested areas and fully developed residential areas, Beasley and Hepinstall-Cymerman were able to compare species abundance across the three site types. After accounting for the effects of natural variations that influence bird habitat, Beasley and Hepinstall-Cymerman found that Blue-headed Vireo, Ovenbird, and Worm-eating Warbler are particularly sensitive to urban development and were most abundant in forested areas. The Eastern Wood-pewee, Indigo Bunting, and Northern Parula were most abundant in suspended developments, suggesting that these species may benefit from moderate clearing, but may not tolerate human presence well.

The researchers also found that the Carolina Wren, Eastern Towhee, Mourning Dove, Northern Cardinal, Red-bellied Woodpecker, and White-breasted Nuthatch were more abundant in both suspended developments and residential sites than in forests, suggesting a tolerance of low intensity development, or perhaps even a benefit in the case of the Carolina Chickadee and Tufted Titmouse, which were most abundant in residential sites. Still other species were roughly equally common in all landscape types. Overall, the researchers were able to compare species abundance in forested, suspended development, and residential sites for more than 25 bird species.

One of the most interesting findings of this study is that there is actually an observed increase in species richness (i.e., total number of different bird species) and abundance associated with suspended developments. This is likely because suspended development sites have undergone comparatively low levels of disturbance, which allows existing species to continue to inhabit the area, while opening up new habitat for other bird types.

As the researchers state in an article for publication in a science journal: “The increase in heterogeneity [in suspended development sites] is enough to draw in a number of new species, but it does not exclude many of the original forest species. Many of the modeled species were tolerant of, or even positively influenced by the changes associated with development, and of those that were negatively affected, none were completely absent from developed landscapes.” This is demonstrating the varied effects of human activity on bird populations, where the influence of urban development is highly dependent on the specific bird species.

Beasley and Hepinstall-Cymerman are currently working to make this research relevant for conservation efforts. For example, future research might be able to identify a threshold of development that is tolerable to some species, providing guidelines for urban planners. Research might also be able to identify whether or not modification of human activities or neighborhood design changes could positively affect bird populations.

In any case, it is increasingly evident that all human impact is not negative for wildlife, and in some cases, may even improve diversity. Camille Beasley says about the implications of this research for Macon County and the surrounding areas: “While preservation of contiguous forest is essential for some species, areas developed by humans are capable of supporting diverse bird communities, especially if they keep impacts low and maintain some native habitat. Many neighborhoods in the Franklin area seem to achieve this effect, and although controlling urban sprawl remains ever important, this low intensity approach may be worthwhile to explore for future developments.”

Do you have observations about bird populations in forested areas, suspended developments, or fully developed areas of Macon County? If so, we would love to hear from you.


This column is produced by members of the Coweeta Listening Project (CLP), a branch of the Coweeta Long Term Ecological Research Program. Views expressed here are not representative of the USDA Forest Service or the Coweeta Hydrologic Lab. Please share questions, comments, or suggestions for future topics at cwtlistn@uga.edu or Coweeta Listening Project, UGA, 210 Field St., Room 204, Athens, Georgia 30602.


Original Citation: Coweeta Listening Project. The Franklin Press. Column on "Science, Public Policy, Community." Page B4. December 6, 2013.