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Accuracy and Precision of Estimating Age of
Gray Wolves by Tooth Wear

Discussion


Limited research has been conducted on the validity of either cementum annuli or tooth wear as aging techniques for wolves and coyotes (C. latrans). Validation studies are expensive and few reference specimens of known-age wild specimens are available. Both techniques need more evaluation with known age specimens. The limited published evaluations suggest that accuracy of age estimates for wolves and coyotes from tooth wear are comparable to estimates from cementum annuli, but precision is generally believed to be lower for tooth wear. Linhart and Knowlton (1967) found a strong positive correlation between the 2 techniques when used on coyotes. Bowen (1982) found that coyote ages based on the 2 techniques agreed within 2 years for coyotes up to 9 years old. Goodwin and Ballard (1985) found cementum annuli to be an accurate technique for aging wolves, but it was impractical for use on live wolves because it required canine teeth. Ballard et al. (1995) compared estimates of ages based on cementum annuli from wolf canines and premolars using 2 types of stain and found significant differences between the 2 teeth in annuli counts with one of the stains. Landon et al. (1998) concluded that tooth wear was accurate for aging wolf pups and adults to within 4 years, but noted errors up to 6 years.

We were less precise in our estimates of age from tooth wear than cementum annuli for wolves ≤3 years old (Figs. 3, 4), but precision of the 2 techniques was comparable for wolves ≥9 years of age (Figs. 3, 4, Table 2). Our age estimates from tooth wear for wolves <3 years old were either correct to a single year class or were 1-2 years over actual age. For wolves ≥3 years old, 2 of our 3 readers tended to over estimate age by 1-2 years. Estimates from premolar cementum annuli were ±1 year of known age for wolves up to 3 years old, and 1-3 years under actual age for wolves up to 14 years old. The major advantage of using tooth wear as an estimator of age is that it is noninvasive, places a minimum of stress on living wolves, and requires no damage to museum specimens.

The lack of readers skilled in estimating age from tooth wear, and no written or illustrated guides to train readers, are valid concerns. All techniques available for estimating the age of wolves and other carnivores have elements of subjectivity that require training to produce consistent results. The only guide to estimating age from tooth wear for canids that we are aware of is for coyotes (Gier 1957). Linhart and Knowlton (1967) found a strong positive correlation between Gier's (1957) tooth wear and cementum annuli. Bowen (1982) found tooth wear to be accurate for 15 of 20 coyotes aged 1 and 2 years, but it tended to under-age coyotes ≥3 years old by 1 or 2 years. Landon et al. (1998) noted that variation among readers estimating wolf ages from cementum annuli was related to the experience of readers. Harshyne et al. (1998) in their evaluation of cementum annuli for aging black bears (Ursus americanus) found that a written and illustrated manual was a useful training tool.

We provide descriptions of progressive tooth wear and charts showing stages of wear typically found on incisors, canines, and carnassials of wolves that can be compared to teeth of living wolves or preserved specimens. We also have photographs (available from the first author) of wolf skulls showing wear on incisors and canines typical of age classes that can be used with the written descriptions and our charts. Our use of teeth from Alaska to age wolves from Minnesota and Ontario suggests that patterns of tooth wear may be similar among wolves from distant regions with different prey. Additional study of this issue is needed.

We estimated the age of 15 of 20 (75%) known-aged wolves to within 2 years of their actual age using tooth wear. The maximum error was 5 years for an atypical wolf with an underbite. When 2 wolves with atypical tooth wear were not considered, we aged 15 of 18 (83%) known-aged wolves to within 2 years of actual age, with a maximum error of 4 years.


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