Reproductive History Reconstructions of Black Bears

The years in which a female black bear has successfully reared cubs can sometimes be identified by the presence of characteristic indicators in tooth cementum. Cub rearing is accompanied by a diminished production of the more abundant, lightly staining cementum of the spring and summer growing seasons. Pictured at left is a black bear PM1 tooth section (cementum age 13 years, month of kill June) that shows strong evidence for cub rearing. 

Matson’s has developed proprietary criteria to identify cub rearing based on microscopic examination of sows with known cubbing years. We have successfully applied these criteria to reconstruct reproductive histories for thousands of adult female black bears.

Applications and Complications

The identification of cub rearing years permits an estimate of the age of first reproduction as well as reproductive potential. However, not all reproductively active female black bears have cementum with identifiable cub year indicators. Indicators often become less evident with age, preventing a full assessment of an older bear’s reproductive history even though indicators are present in younger years. To date, the technique only appears to be useful for black bears, and not other bear species.

Recommendations

Treat reproductive history reconstructions as approximations. The cementum indicators for the first years of cub rearing are usually the most evident ones, and therefore early reproductive history may yield the most useful data from the method. Use the largest possible sample size to estimate the population’s reproductive potential based upon cementum evidence. The estimate will undoubtedly be low, because indicators are less visible and likely more often missed in the cementum of older bears.

Brown Bear Reproductive Histories
Matson’s studied the potential for reconstructing reproductive histories in brown bears. Photographs were used to directly measure cementum layer thicknesses, which were then tabulated for mathematical calculation to detect differences that were not visually evident. Among the 29 female brown bears with part or all of their reproductive histories known, we correctly identified only 13 of 62 known cub years. Because of this low accuracy, it was concluded that brown bear reproductive histories cannot be reconstructed using the method shown to be successful for black bears. These findings were presented in a poster at the Eleventh International Conference on Bear Research and Management in Gatlinburg, Tennessee. Please see the Publications page of this site, Matson et al. 1998.