The Reproductive Biology of Female Grizzly Bears in the Northern Continental Divide Ecosystem with Supplemental Data from the Yellowstone Ecosystem

January 1, 1994
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We analyzed reproductive performance and litter survival for all Northern Continental Divide Ecosystem (NCDE) grizzly bears (Ursus arctos) killed or radioinstrumented, 1969-91. Reproductive tracts of 48 female grizzly bears from Montana and Wyoming were described morphologically and examined for corpora lutea and graafian follicles to estimate reproductive potentials for bears in the conterminous United States. The average number of corpus lutea was 2.29. Average cub and yearling litter size was 2.14 and 2.34. Cub survival in the NCDE was 0.887 and yearling survival was 0.863. Sixteen reproductive intervals in the NCDE from 10 individual bears averaged 2.69 years. The minimum age of reproduction in the NCDE varied from 4 to 7 and averaged 5.7 years. Survival of known first litters was not less than survival for litters of experienced females.

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