Analysis of error from cementum-annuli age estimates of known-age Pennsylvania black bears

Cementum-annuli counts are considered the most accurate indicators of age for black bears (Ursus americanus), but tests of the technique have lacked large sample sizes of known-age teeth, and sources of error are not well documented. We estimated ages from cementum-annuli counts of 671 teeth from 521 Pennsylvania black bears and compared the estimated ages to their known age. We evaluated teeth aged during 1983-91 with aging criteria different from the criteria used during 1992-96, but we found no differences (M: P = 0.125; F: P = 0.748). Overall, 8.1% of the known-age teeth were aged incorrectly, and we found no differences in error distributions between sexes (P = 0.126). For both sexes, percent error increased as age class increased (Ps≤0.010). The number of incorrectly aged teeth was greater than expected (Ps ≤ 0.104) in black bears captured during September-November (M = 11%, n = 198; F = 13%, n = 181) than during March-May (M = 3%, n = 76; F = 4%, n = 49) and June-August (M = 3%, n = 120; F = 2%, n = 45). Of 51 incorrectly aged teeth we reevaluated, 19 (37%) were aged incorrectly because of irregular tooth characteristics to which standardized aging criteria could not be applied accurately. Thirteen (25%) probably would have been aged correctly via aging criteria revised in 1992, 13 (25%) had no discernible reason for being incorrectly aged and may have been mislabeled, 5 (10%) were broken during extraction, and 1 (2%) was aged incorrectly by the tooth reader even though the annuli were normal and distinct. We concluded that counting cementum annuli is a valid technique for aging Pennsylvania black bears.