Abstract
A technique for age determination based on the dry weight of the optic lens was tested in Smith's red-backed vole, Eothenomys smithii. The model equation W=a+blog10A (W : lens weight in mg, A : age in days, a and b : parameters to be estimated from data) was applied to our data from 65 known-age laboratory-reared voles. As a result, the predicted age in days (Â) at a given lens weight (W) could be calculated from the equation Â=10(W+1.415)⁄2.131. For example, an individual with a lens weighing 3.22 mg was estimated as having a predicted age of 150 days, and the 95% confidence interval at 150 days was calculated to be 17 days (142-159 days, or 11.3% of the predicted age) for the mean prediction and 144 days (94-238 days, or 96.0% of the predicted age) for the individual prediction. Lens weight can, it appears, provide the best age criterion at present, particularly in rodents with rootless molars such as E. smithii.
