Effects of Hemlock Woolly Adelgid on Breeding Birds at Fort Indiantown Gap, Pennsylvania

Abstract

To determine how Tsuga canadensis (eastern hemlock) decline caused by Adelges tsugae (hemlock woolly adelgid) affects bird communities in Pennsylvania, we surveyed breeding birds in hemlock and forested non-hemlock habitats in 2003 and 2004 at Fort Indiantown Gap, PA and monitored nesting Empidonax virescens (Acadian Flycatcher), a hemlock specialist in Pennsylvania. Of the nine species more abundant in hemlocks than other forested habitats, only two, the Acadian Flycatcher and Dendroica virens (Black-throated Green Warbler), were positively associated with living hemlocks. Contopus virens (Eastern Wood-pewee), Myiarchus crinitus (Great-crested Flycatcher), and Hylocichla mustelina (Wood Thrush) were negatively associated with the amount of living hemlocks and were apparently benefiting from the increased number of dead trees and canopy gaps associated with the adelgid infestation. Acadian Flycatcher nest sites had more living hemlocks and were less impacted by adelgid than random sites. Nest success did not differ by habitat variables. Initially, hemlock decline will negatively impact hemlock specialists while providing habitat for opportunistic species. Some specialist species might persist by shifting habitats, but long-term studies are needed.