Living on the Edge: Risk of Predation Drives Selection of Habitat and Survival of Neonates in Endangered Sierra Nevada Bighorn Sheep

MS Thesis, Shannon Forshee (2015-2018)

Long-term viability of endangered populations requires development of effective management strategies that target the population vital rate with the highest potential to influence population trajectories. When adult survival is high and stable, juvenile recruitment is the vital rate with the greatest potential to improve population trajectories. For my thesis I examined how lactating Sierra Nevada Bighorn sheep (Ovis Canadensis sierra) balance forage and predation risk during the neonatal period. I first identified resource selection strategies employed by lactating females to promote survival of neonates and then determined the primary factors affecting survival of neonates. I found lactating females selected for habitat that, despite decreased access to high quality forage, reduced the risk of predation by mountain lions. Understanding the availability of high quality neonate rearing habitat is an important consideration in restoring bighorn populations. My predictive resource selection function models will assist managers in identifying habitat that is most likely to meet the lambing needs of lactating bighorn females. I also found that despite the efforts of lactating female to protect neonates from risks of predation, predation was the strongest factor contributing to variable survival of neonates across subpopulations. I determined that neonates become less vulnerable as they age, were most vulnerable if they were born before the peak birth pulse (April) and if lactating females selected habitat farther from the safety of escape terrain. My work is the first to examine factors affecting selection of neonatal habitat by lactating females and survival of neonates within Sierra bighorn sheep populations. My results have elucidated potential management strategies that may inform recovery actions.