Modeling nutritional carrying capacity for translocated desert bighorn sheep in western Texas

Restoration of desert bighorn sheep (Ovis canadensis) is proceeding in seve ral western states. Measurement of nutritional resources (quality and quant ity) is not normally conducted to assess future and present translocation s ites, although it has been recommended generally for evaluation of ungulate habitat. We estimated nutritional carrying capacity (based on nitrogen in forage species) of three mountain ranges in Trans-Pecos Texas where desert bighorn sheep have been translocated. We used an explicit nutritional const raint model to estimate carrying capacity on a seasonal basis. Although dro ught conditions prevailed during the study period, bighorns were not limite d by quantity of vegetation. However, forage biomass of high nutritional qu ality (>1.5% N) was very low (<9 kg/ha in spring; <1 kg/ha in all other sea sons). Consequently, there appeared to be inadequate forage of high N conte nt for bighorns to meet reproductive requirements in some seasons. Estimate s generated using the explicit nutritional constraint carrying capacity mod el appeared to be realistic relative to observed densities. Nutritional sam pling and modeling can predict potential carrying capacity on areas schedul ed for restoration or on ranges already stocked, predict effects of managem ent on carrying capacity, and allow managers to compare among restoration s ites. We recommend that desert bighorn managers focus on monitoring the abu ndance of high-quality (%N) forage species, especially during periods of dr ought or higher nutritional requirements (e.g., lactation, post-weanling gr owth).