Is weight a reliable index to age in microtine rodents?

Frequency distributions of "age" classes based on body weights and on molar development and morphology are compared both within and among years in samples of . Weight class limits that give the best fit to molar class frequencies vary from year to year. Body weight is a poor predictor of the molar class of an individual. Weight class limits determined from all age classes in a sample gave poor results when applied to the sexually mature component only. In interyear comparisons, body weight and molar morphology gave conflicting views of differences in age structure, and hence of the dynamics of the population. Body weight should be used with caution an an index to age of Clethrionomys, and by extension, to other microtine rodents.