We examined relationships between reproductive performance of female Minnesota black bears (Ursus americanus) and various potential indicators of nutritional condition during late hibernation. Litter size (n = 101 litters) was influenced more by litter order (first or subsequent) than by maternal condition, except perhaps in very large females. An increased proportion of male cub births corresponded with increased maternal weight and serum alkaline phosphatase (ALKP) and decreased serum creatinine (CR). Weight and growth of cubs and yearlings were closely related to mother's size; they also correlated positively with maternal ALKP, and negatively with serum total protein (TP), and mean corpuscular volume (MCV). Cub survival was affected only when mother's weight 2 months postpartum was below about 65 kg. No juvenile females (2-8 years old) weighing < 41 kg in March produced their first cubs the following spring, but 57% of those above this threshold weight produced cubs. Litter frequency and yearling recruitment were unrelated to maternal condition. Life history parameters of black bears appear to respond to declining nutrition in the following sequence: (1) litter size declines, then stabilizes across a broad range of maternal weights; (2) age of first reproduction increases; (3) juvenile survival decreases; (4) first-year cub survival decreases; and (5) litter frequency decreases. Better definition of these relationships, particularly at nutritional extremes, will likely require collaborative efforts of researchers studying diverse populations.
- Volume 9
- Issue
- Pages 481-496
- Publication Date 1 January 1994
- DOI 10.2307/3872736
- File Size 696.27 KB
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