Factors Influencing Winter Mortality Risk for Pronghorn Exposed to Wind Energy Development

Evaluating the influence of energy development on pronghorn (Antilocapra americana) winter mortality risk is particularly critical given that northern populations already experience decreased survival due to harsh environmental conditions and increased energetic demands during this season. The purpose of our study was to evaluate pronghorn mortality risk over 3 winters (2010, 2010-2011, 2011-2012) on a landscape developed in 2010 for wind energy production (Dunlap Ranch) in south-central Wyoming, United States. We obtained locational data and survival status of 47 adult female pronghorn captured and equipped with Global Positioning System (GPS) transmitters. Overall, 17 pronghorn died during winter seasons, with 76.4% (13) of deaths occurring during the winter with highest snow accumulation (2010-2011). Survival (Ŝ) was lowest in winter 2010-2011 (Ŝ = 0.53, 90% confidence interval [CI]: 0.37-0.70) and highest in winters 2010 (Ŝ = 0.97, 90% CI: 0.92-1.00) and 2011-2012 (Ŝ = 0.91, 90% CI: 0.82-1.00). We modeled mortality risk for pronghorn using Cox's proportional hazards model inclusive of time-dependent and time-independent covariates within anthropogenic, environmental, and wind energy variable classes. Across winters, pronghorn winter mortality risk decreased by 20% with every 1.0-km increase in average distance from major roads (hazard ratio = 0.80, 90% CI: 0.66-0.98), decreased by 4.0% with every 1% increase in average time spent in sagebrush (Artemisia spp. L.; hazard ratio = 0.96, 90% CI: 0.95-0.98), and decreased by 92% with every 1 unit (VRM × 1000) increase in terrain ruggedness (hazard ratio = 0.08, 90% CI: 0.01-0.68). Pronghorn winter survival was not influenced by exposure to wind energy infrastructure; however, pronghorn survival may be impacted by larger-scale wind energy developments than those examined in our study. We recommend wildlife managers focus on conserving sagebrush stands in designated pronghorn winter range.