We studied reproduction by black bears (Ursus americanus) in 3 dissimilar Maine study areas from 1982 to 1991. Nuts of American beech (Fagus grandifolia) were the primary fall food source in Spectacle Pond, a major fall food in Stacyville, and rarely available in Bradford. We visited 396 dens, including 303 dens of 96 adult females, and examined 154 newborn litters. Alternate-year beechnut crop failures appeared to maintain reproductive synchrony at Spectacle Pond, where 73 of 77 (95%) litters were produced on odd-numbered years following abundant beechnut crops. Most bears at Spectacle Pond began to reproduce at 6 years of age, and had 2-year intervals between litters, even after litter loss. Eighty percent of breeding females (i.e., adults without cubs) produced litters at Spectacle Pond when beechnuts were abundant, but breeding females lost weight and only 13% produced litters when beechnuts were scarce. Reproductive synchrony was less pronounced at Stacyville and Bradford, where most bears began to produce litters at 4 years of age, and generally produced subsequent litters 1 year after litter loss. At Stacyville and Bradford, bears maintained stable weights regardless of beechnut abundance, and most breeding females produced litters every year. Where bears depend upon few fall foods, food failures may synchronize female reproductive schedules and impact population age structures. Adequate understanding of bear reproductive biology includes estimates of litter losses and resulting inter-litter intervals for projections of cub production.
- Volume 9
- Issue
- Pages 471-479
- Publication Date 1 January 1994
- DOI 10.2307/3872735
- File Size 352.28 KB
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