Survival of desert bighorn sheep in Sonora, Mexico

Abstract Numbers and distribution of desert bighorn sheep ( Ovis canadensis mexicana ) have significantly declined from historic levels throughout their range in Mexico. Consequently, we documented survival rates of adult female and male desert bighorn in Sonora from 2019 to 2021, emphasizing adult females given the sensitivity of population rate-of-increase to adult female survival, and further evaluated survival with respect to precipitation patterns. Survival in 2019 (females = 0.88; males = 0.57) was comparable to other North American desert bighorn populations, but declined to the lowest levels documented for adult desert bighorn during severe droughts in 2020 and 2021 (≤0.50). Survival was most strongly associated with total annual precipitation; odds of desert bighorn survival increased 1.01× for each 1 mm increase in total precipitation. Survival was also influenced by precipitation during the post-monsoon period, which coincides with the periods of highest energetic demands on bighorn. Survival-days were similarly influenced by precipitation during these same time periods, as well as landscape greenness during the post-monsoon period. Recovery of desert bighorn will be challenging due to the impact of precipitation on survival and the increasing frequency and severity of drought in Sonora, as management options to mitigate drought-induced declines are extremely limited.