Lutra 52(2)_Haarsma & Van Alphen_chin spots & pond bats_2009

Chin-spot as an indicator of age in pond bats

In field studies of animal populations, it is often useful to be able to assess the age of an individual. In this paper we investigate the use of chin-spots as an indicator of age in pond bats (Myotis dasycneme). During six years of research, from 2002 to 2008, we captured more than 2,500 pond bats. To test whether the chin-spot can be used, we gathered data on chin-spot colour and other indicators of age, such as dental wear, degree of fusion of phalangeal epiphyses and reproductive status. We tested the correlation between chin-spot colour and these indicators of age. We also studied the transformation of these characteristics during bats’ life course and therefore between different age classes. We found significant correlations between the colour of the chin-spot and other known age indicators. The results showed a significant relation between colour and the number of days between the first and the last capture. The longer the period between two capture events, the larger the change in colour of the chin-spot. Animals of a known age, captured as juveniles, showed a transformation in coloration from deep purple (class 5) to light-coloured (class 1) over an average time period of two to four years. Most of the juvenile pond bats had a chin-spot coloration in class ‘4’ or ‘5’, most sexual immature animals in class ‘3’ and most mature animals in class ‘1’. We conclude that the colour of the chin-spot is a reliable predictor of the age class of pond bats.