Effect of White-Tailed Deer on Songbirds within Managed Forests in Pennsylvania

Abstract

White-tailed deer (Odocoileus virginianus) populations have been maintained at high densities in Pennsylvania for several decades with unknown effects on songbirds and their habitats. I evaluated effects of white-tailed deer density on songbird species richness, abundance, and habitat. I simulated 4 deer densities (3.7, 7.9, 14.9, and 24.9 deer/km2) within individually fenced enclosures on 4 65-ha forest areas in northwestern Pennsylvania. Within all enclosures, 10% of the area was clear-cut and 30% was thinned. Enclosures were subjected to 10 years of deer browsing, 1980-90, at the 4 simulated densities. I conducted bird counts in 1991. Varying deer density had no effect (P > 0.1) on ground- or upper canopy-nesting songbirds or their habitat, but species richness of intermediate canopy-nesting songbirds declined 27% (P = 0.01) and abundance declined 37% (P = 0.002) between lowest and highest deer densities. I did not observe the eastern wood pewee (Contopus virens), indigo bunting (Passerina cyanea), least flycatcher (Empidonax minimus), yellowbilled cuckoo (Coccyzus americanus), or cerulean warbler (Dendroica cerulea) at densities >7.9 deer /km2, and the eastern phoebe (Sayomis phoebe), and American robin (Turdus migratorius) were not observed at 24.9 deer/km2. Threshold deer density for effect on habitat and songbirds within managed (100-yr rotation) forests was between 7.9 and 14.9 deer/km2.