Impacts of oil-and-gas development in the Eagle Ford Shale on quail and other birds

Many North American birds have been declining across their geographical ranges for the past few decades due to habitat loss and fragmentation. South Texas is one of the last remaining strongholds for northern bobwhite (Colinus virginianus; hereafter bobwhite) and scaled quail (Callipepla squamata) populations in the US. The region is also important for conservation of all birds because it contains large tracts of unfragmented habitat, mostly in the form of privatelyowned ranches. However, the recent development of the Eagle Ford Shale hydrocarbon formation in this region has the potential to negatively impact quail and other avian species and their habitat. The objective of this study was to determine how bobwhites, scaled quail, and other avian species respond to localized oil-and-gas disturbance. My study took place on 2 private ranches located in Dimmit County, Texas during March – September (2015 and 2016). I trapped and radio-marked bobwhites and scaled quail in 2 focal areas along an oil-and-gas exploration corridor (disturbed treatment) and 2 focal areas along corridors where relatively little Eagle Ford Shale exploration activities have occurred (relatively undisturbed treatment). Point counts and nest searches for all birds were also conducted in these focal areas. Indirect oil-and-gas disturbance was quantified with a sound level meter and traffic counters. Noise propagation for 2 frequencies (250 Hz and 1,000 Hz) was modeled during each month of the study with field measurements and noise propagation software. I examined quail site selection to roads and sound levels, and quail home range and core area size, seasonal adult survival, nest success, and density in response to disturbance from oiland- gas activity. Bobwhites and scaled quail selected for areas 0 m–200 m and >425 m from the primary corridor road, respectively. In the relatively undisturbed area, bobwhites and scaled quail selected for areas 0 m–425 m and 0 m–300 m from primary roads, respectively. Bobwhites and scaled quail avoided sites with sound levels >1.6 dB and >2.2 dB above ambient levels at the 250 Hz frequency level, respectively. At the 1,000 Hz frequency level, bobwhites and scaled quail avoided sites with sound levels >2 dB and >3.2 dB above ambient levels, respectively. I found no linear relationship between home range and core area size and disturbance (sound levels and vehicle passage rates) for either species of quail (P > 0.359 for bobwhites, P > 0.127 for scaled quail), although mean home range and core area sizes of both quail species were numerically larger in disturbed area than undisturbed areas. Seven-month (Mar – Sep) survival probability for bobwhites and scaled quail was 11.9 ± 5.1% and 43.8 ± 9.0%, respectively. I found no relationship between seasonal survival probability and disturbance for either species of quail. Probability of nest success for bobwhites and scaled quail was 49.8 ± 12.4% and 38.1 ± 18.9%, respectively. For bobwhites, probability of nest success decreased as sound levels (dB) at 250 Hz increased. I found no relationship between probability of nest success and disturbance for scaled quail. However, average sound levels (at 250 Hz) at scaled quail nests only ranged from ambient to 1 dB above ambient, whereas levels at bobwhite nests were over a larger range. Density of all quail was not significantly different between disturbed and undisturbed areas. I examined avian nest-site selection, nest success, and density in response to oil-and-gas disturbance. Birds preferred nest sites with sound levels 0 dB–2.6 dB above ambient levels at the 1,000 Hz frequency level in both study years. I found no effect of treatment (P = 0.144) on apparent nest success. However, apparent nest success was 28% lower in disturbed areas (41.2 ± 11.9%) than in undisturbed areas (69.2 ± 12.8%). I found no relationship between disturbance (noise levels and vehicle passage rates) and apparent nest success. Density of all bird species was greater in disturbed areas (6.0 birds/ha) than in undisturbed areas (1.8 birds/ha). Grassland associates and cosmopolitan species constituted a greater proportion of total density in disturbed areas than in undisturbed areas. In addition to outright habitat loss due to conversions of rangeland to oil-and-gas infrastructure, the apparent indirect influence of oil-and-gas activity on site use and demographics of quail and other avian species is an important management consideration as production in the Eagle Ford Shale region continues