Kristin Denryter, Thomas R. Stephenson, Kevin L. Monteith
Abstract Nutritional resources during summer are important for supporting fat accretion, growth, survival, and reproduction and generally set upper limits on population productivity. We aimed to quantify the nutritional resources in plant communities available to endangered Sierra Nevada bighorn sheep ( Ovis canadensis sierrae ; hereafter Sierra bighorn) during summer and evaluate whether forage quantity (biomass) and forage quality (digestible energy [DE], crude protein [CP]) were adequate to meet nutritional requirements of Sierra bighorn in California, USA. From June through August 2017–2018, we sampled forage biomass in 5 plant communities (barren, dry shrub, herbaceous dry, herbaceous wet, and wet shrub) available to Sierra bighorn using double‐sampling techniques, and assayed 2018 forage samples for DE and CP content. We related DE and CP content within plant communities to nutritional requirements of lactating Sierra bighorn. All 5 plant communities sampled provided adequate CP to meet nutritional requirements for lactation, whereas only 4 of 5 plant communities provided adequate forage biomass and only 2 of 5 plant communities provided adequate DE. Wet shrub plant communities provided the greatest forage biomass and high levels of CP and DE for Sierra bighorn during summer, and barren communities provided the least forage biomass. Combined forage biomass and forage quality data suggested nutritional value was greatest in wet shrub communities, followed by herbaceous wet, dry shrub, herbaceous dry, and barren. Our findings indicate that DE and, to a lesser extent, forage biomass during summer set an upper limit for population productivity of Sierra bighorn, but CP did not. Understanding the nutritional value of plant communities available to Sierra bighorn during summer can help inform recovery efforts, including translocations, and provide a biological basis for recovery goals relative to nutrition.