Effects of Marcellus Shale Development on Songbird Abundance and Habitat Use in Northcentral Pennsylvania Forests

Open Access
Barton, Ethan Patrick
Graduate Program:
Wildlife and Fisheries Science
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 29, 2014
Committee Members:
  • Margaret Brittingham Brant, Thesis Advisor
  • Walter Matthew Tzilkowski, Thesis Advisor
  • Duane R Diefenbach, Thesis Advisor
  • Michael Gerard Messina, Thesis Advisor
  • Marcellus
  • shale gas
  • forest
  • songbirds
  • biotic homogenization
  • habitat fragmentation
Due to recent instability in the international petroleum products market, American industries are seeking to develop domestic sources of energy, and foremost among these domestic sources is natural gas. The Marcellus Shale formation in the northeastern portion of the United States contains a vast portion of the natural gas reserve of North America; the northeastern US also contains many large core forest reserves important for breeding songbirds. Within the last decade, development of wells within the Marcellus has rapidly expanded, and the number of wells permitted for drilling has increased steadily. In forested areas, Marcellus development creates large disturbances and causes substantial fragmentation, but the landscape matrix remains dominated by stands of mature forest. I examined the effects of Marcellus Shale gas development on songbird abundance and habitat use surrounding 30 well pads, mean size 2 hectares, placed within an extensive forest landscape in northcentral Pennsylvania. I used fixed-radius point counts to assess songbird abundance relative to well pads at four distances from the pad edge: two points in new edge habitat (0m and 50m) created by pad development and two points in remnant post-development interior habitat (150m and 250m), which served as a reference. I conducted bird and vegetation surveys in both northern hardwood and mixed oak habitat. To determine whether bird abundance and species composition differed between edge and reference points, I analyzed the aggregate avian community at edge and interior points and also built linear mixed models for three guilds of species based upon habitat preference: forest interior, early-successional, and synanthropic species. I also constructed linear mixed models for individual bird species within the guilds observed at ≥50% of field sites. Avian communities differed between forest interior and pad edge, and they also differed by forest habitat type (northern hardwood or oak) overall and at interior reference points. However, communities did not differ by forest habitat type at edge points, indicating biotic homogenization may be occurring near well pads. Forest interior species were significantly less abundant near the pad edge relative to interior reference points. Interior habitat associates such as black-throated green warblers (Setophaga virens), black-throated blue warblers (Setophaga caerulescens), ovenbirds (Seiurus aurocapilla), red-eyed vireos (Vireo olivaceus), hermit thrushes (Catharus guttatus), and scarlet tanagers (Piranga olivacea) were less abundant at edge points than within the forest interior. In contrast, synanthropic species were more abundant near pad edges than at interior points. American robins (Turdus migratorius) were more abundant within 100m of well pad edges than at reference points within the forest interior surrounding well pads. Distance from edge was not a significant predictor of abundance for the early successional species guild or individual species associated with the guild. Common yellowthroats (Geothlypus trichas) and eastern towhees (Pipilo erythrophthalmus), two species associated with early successional habitat, did not exhibit a detectable response to development. I took nested-plot vegetation samples at points surrounding well sites to assess vegetative changes near well pads as a possible explanation for bird distribution. Average canopy cover, mean litter depth, the number of tree stems >8cm diameter at breast height, and the number of small sapling stems <2.5cm were significantly lower at the immediate pad edge (0m) than at sample points of greater distances, but no other differences were detected. My results suggest development has not largely altered vegetation beyond the immediate edge, but the length of post-disturbance time elapsed may be insufficient for vegetative edge effects to be detectable. Absence of increased sapling density near well pads and lack of a detectable positive response to development by early-successional guild members present evidence Marcellus development is not currently creating early successional habitat. Instead, unconventional gas development appears to be creating a degree of radiative habitat loss beyond what forest is removed for pad construction: forest interior birds are significantly less abundant in forest within 100m of well pad edges. Edge and generalist species, which were previously rare or absent within the forest landscape, are moving into new edge habitat around Marcellus well pads, suggesting an ongoing shift in the bird community near well pad development and possible biotic homogenization as common generalist species replace less common forest specialists.