Age determination of the bank vole Clethrionomys glareolus Schreber, 1780

Abstract

Many methods of age determination have been devised for use on large mammals. An attempt was made to discover whether they were applicable to a small species, how accurate the methods could be and whether the age determination criteria were influenced by environmental factors. This study was based on 199 known-age specimens of the mainland bank vole, Clethrionomys glareolus britannicus (Miller), and 169 specimens of the Skomer vole, C. g. skomerensis (Barrett-Hamilton).These two laboratory raised samples were used to assess the relative accuracy and reliability of different age determination criteria. Morphological characters which were used for ageing included: body weight, body measurements, skull measurements, molar root development, tooth wear, fusion of epiphyses, baculum, pelage, and dry weight of the eye lenses. Changes in these characters were studied through 18 months of age. Laboratory study showed that the dry weight of the eye lens gave the best results for ageing. Development of the molar roots found to be highly correlated with age, as was tooth wear. Fusion of ten sets of epiphyses combine to give a high degree of accuracy in age-determination up to the age of 14 months. The correlation of skull measurements, moult, body measurements, and body weight with age was also studied. Tables were prepared for estimating the age of the two subspecies from every character used and 95% confidence limits were attached to the results. A low-calcium diet was given to 60 known-age mainland bank voles hut there was no measurable effect even on homes and teeth. Seventy three known-age mainland hank voles were released in outdoor enclosures. Growth data of 18 of them were analysed and compared with data from laboratory-raised animals. The results were in agreement with the latter, except in regard to tooth wear and to some extent in root growth.