| Oil and natural gas development in the Intermountain West of North America has expanded over the last two decades, primarily within sagebrush ( Artemesia spp.) dominated landscapes. Although the effects of energy development on high profile game species such as the greater sage-grouse ( Centrocercus urophasianus) have been documented, studies examining responses of non-game birds are lacking. Simultaneously, many songbirds that breed within sagebrush steppe habitats have shown range-wide population declines that are likely due to widespread habitat loss and alteration. I evaluated songbird abundance, species richness, nest survival and offspring quality across gradients of oil and natural gas development intensity at three energy fields in the Upper Green River Basin, WY, USA during 2008--2009. While simultaneously accounting for important habitat attributes, increased well density was associated with decreases in Brewer's sparrow ( Spizella breweri), sage sparrow (Amphispiza belli ), and vesper sparrow (Pooecetes gramineus) abundance. Horned larks (Eremophila alpestris) increased with well density in the Pinedale Anticline natural gas field. Sage thrashers (Oreoscoptes montanus) showed no response to energy development. Species richness was not significantly affected by well density. Additionally, I tested two alternative hypotheses for why oil and natural gas development influences songbird populations in western Wyoming: increased nest predation or food limitation. The probability of daily nest survival for Brewer's sparrow, sage sparrow, and sage thrasher decreased with greater well densities and increased proximity to well pads, and avian nest predator abundance increased slightly across energy development gradients, supporting a nest predation hypothesis. Additionally, shrub vigor decreased with increasing energy development, which could decrease insect prey availability and impact parental investment in offspring through decreases in clutch size and (or) offspring provisioning. Clutch size did not vary with energy development, but average nestling mass for the sage thrasher (the largest of the study species) decreased significantly with increasing development, lending partial support to the food limitation hypothesis. My results indicate that regional declines of some songbird species, especially sagebrush-obligates, may be exacerbated by increased energy development and suggest that avian declines within energy fields may be influenced by increased susceptibility to nest predation and changes in food resource availability. |
