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Forest songbird communities

Vanessa Fox, Dana Dudle, Bryan Helm, David Pope, and Aaron Randolph
Biology Department and Science Research Fellows, DePauw University
Summer 2004

Introduction
Here we present baseline data on forest songbird communities in the DePauw Nature Park.  Our goal was to survey the songbird population and assess the quality of forest habitat in the park.  

Methods
We set up study plots in three forested sites:  Arboretum (ARB), Quarry South (QS), and Quarry Hillside (QH).  We surveyed bird populations using the territory-mapping method.  Each site was surveyed four times during May and June between 6 and 10 a.m.  During each survey, we recorded locations of songbirds.  Clusters of observations over multiple visits were used to identify songbird territories.  Population sizes for songbird species were estimated based on the number of territories within each site. 

We searched for and monitored nests following BBIRD protocol.  Nests were checked every 3 to 5 days to monitor their contents and determine their fate.  Successful nests produced at least one host fledgling whereas failed nests had no fledglings.  Causes of nest failure included predation, parasitism by Brown-headed Cowbirds, abandonment, and weather.  We estimated daily nest survival rates using the Mayfield method.  

Results and Discussion
The three sites supported a variety of songbird species that are typical of eastern deciduous forests.  

One of the most intriguing results was the presence of Cerulean Warblers at QS.  The Cerulean Warbler is a species of significant conservation concern and requires large tracts of mature closed-canopy forest for nesting habitat, and populations may be declining due to loss of habitat.  Their distributions are patchy within suitable habitat but reasons for this patchy distribution are unknown.  The presence of Cerulean Warblers at QS appeared to be unrelated to differences in forest composition or structure but attests to the importance of maintaining the forest within its existing condition to continue to provide habitat for this bird species.

The dense growth of shrubs in the forest at QH provided suitable nesting habitat for the Indigo Bunting.  Indigo Buntings usually occur in early-successional habitats such as open meadows.  They were common in edge habitat in the ARB, next to the powerline and athletic fields.  Indigo Buntings were more widely distributed throughout the forest habitat of QS.  The distribution of this bird species across a variety of habitats (edge, meadows, and closed-canopy forests) provides an opportunity for future research on fitness consequences of habitat selection within an easily accessible environment close to campus. 

Acadian Flycatchers occurred at all three sites.  This bird species nests in large trees located along moist forest ravines.  We monitored 13 Acadian Flycatcher nests and found fairly high levels of breeding productivity.  Half of the nests failed due to predation or Brown-headed Cowbird parasitism, but the estimated rate of daily nest survival of 95.5% may be sufficient to support a healthy self-sustaining population.  The Acadian Flycatcher is another appropriate species for additional research since it was common at all three sites and their nests tend to be accessible.

Wood Thrushes are common in eastern deciduous forest habitat, and their large bulky nests tend to be easy to find and monitor.  Wood Thrushes were common at QH but were almost absent in the other sites, and their nests were difficult to find.  The differences in forest structure and composition between the sites do not necessarily explain these results, but the Wood Thrush’s unusual distribution merits closer attention in the future.

Overall, the forest habitat in the DePauw Nature Park provides valuable habitat for a variety of songbirds, several of which are of significant conservation concern.