The reproductive characteristics of 241 female black bears (Ursus americanus) ≥3-years-old were examined in east-central Ontario from 1969-1980. During the 12-year period, the percentage of adult females reproducing each year ranged from 13-58 and averaged 38. Litter sizes ranged from 1 to 4 and averaged 1.9 from summer captures and 2.5 from den examinations. Size of litters was positively correlated with both age of the female (P < 0.009) and weight the previous fall (P < 0.001) (N = 28). Fall weights of 20 adult females that produced cubs the following year averaged 97 kg compared to an average of 70 kg for 14 females that did not produce cubs. Weights of 16 of 20 of the former exceeded 80 kg whereas only 4 of 14 of the latter group were that heavy. Females produced their first litters at ages 5-8; the mean age of first reproduction was 6. Age-specific natality rates for females aged 5-18 ranged from 0.36 to 1.50. Females aged 5-7 produced an average of 0.6 cubs/year and females aged 8-18 an average of 1.2 (P < 0.01). Based on 4-8 consecutive years of breeding history, 14 of 15 bears had a 2-year breeding cycle. The male-to-female ratio of cubs produced was 113:100 (N = 96). Of the 68 different adult females checked during the study, 59% produced at least one litter of cubs. However 17 of the 68 bears produced 66% of all litters. Characteristics common to the most productive females were longevity, large size, possession of a home range and low vulnerability to hunters. Because a successful female had a high probability of being successful again, the protection of females with young would be a desired management strategy in heavily hunted populations or populations occupying marginal or fragmented patches of habitat.
- Volume 8
- Issue
- Pages 385-392
- Publication Date 1 January 1990
- DOI 10.2307/3872942
- File Size 362.71 KB
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