Population characteristics and winter ecology of black bears in Coahuila, Mexico

Biology, status, and distribution of black bears (Ursus americanus) in Mexico are poorly under stood. We studied a population of black bears in the Serranias del Burro, Coahuila, Mexico, from 1991 to 1994 to address the hypothesis that the recolonization source for bears in Texas is the Sierra del Carmen range in northern Mexico. We also described aspects of winter ecology in this southerly population. We captured 42 bears (27 M, 15 F) and equipped 28 with radiotransmitters. All pregnant females (n = 13) and 2 of 5 females with yearlings denned, whereas all other bears, including 10 males, remained active during winter. Mean (+/- SE) den entry and exit dates for pregnant females (n = 5) were 25 December (+/- 5 days) and 22 April (+/- 2 days). Mean age at primiparity was 4.5 +/- 0.6 years (n = 4), interbirth interval was 2.0 +/- 0.0 years (n = 3), and litter size was 2.75 +/- 0.25 cubs/female (n = 12). Estimated adult female and cub annual survival rates were 0.94 +/- 0.05 and 0.81 +/- 0.10, respectively, based on radiotelemetry and observation of family groups. Estimates of subadult male survival ranged from 0.88 +/- 0.08 to 1.00 +/- 0.00. We estimated density to be 0.35 bears/km(2) using a modification of the Lincoln-Petersen estimator that employs animal-equivalents. Because of high reproductive rates and lack of anthropogenic mortality, our data were consistent with the hypothesis that the area can serve as a source of bears emigrating to western Texas. Future bear research in this region should focus on determination of the source of emigrating bears, and identification and conservation of corridors linking Mexican and Texan populations of black bears.