Bighorn sheep (Ovis canadensis) were re- introduced into the Black Hills, South Dakota, U.S.A. in 1965. To date limited information exists concerning vital rates of this population. From 2010 to 2013, we estimated survival and cause-specific mortality of 55 adult female bighorn sheep in three herds in the east-central Black Hills. We documented 21 mortalities. Of those, pneumonia (19%) and predation (19%) accounted for most known causes of mortality; however, we were unable to ascertain cause of death for 47.6% of mortalities. We used a known fate analysis in Program MARK to estimate monthly survival; our best approximating model indicated survival differed during May–Jun compared with the remainder of the year. Monthly survival estimates for May–Jun were 0.95 (95% CI = 0.91–0.97) compared with 0.99 (95% CI = 0.98–0.99) for Jul–Apr, and overall annual survival was 0.81 (95% CI = 0.72–0.87). We found little support for the hypothesis that survival was influenced by body mass or nutritional condition (ingesta-free body fat). Our results indicated disease, predation, and other factors predisposing ewes to mortality, especially during and shortly after parturition, were contributors to the current demographic status of this population.
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