Fur clipping as a method for identification in the hazel dormouse, Muscardinus avellanarius: how reliable is it for monthly monitoring?

Fur clipping is a non-invasive method, widely used for marking small mammals to enable them to be individually recognised. Individual identification can be important to estimate minimum population size and home range and to measure survival and movement between captures. Social interactions and breeding, such as frequency of litters, may also be studied. Clipping of the guard hairs to reveal the darker underfur is generally accepted as an ethical and non-invasive procedure and only requires a Natural England level 2 survey licence in the United Kingdom. Less training and resources are needed than for invasive methods such as passive integrated transponders. However, it is unclear how long fur clip marks persist. In this study, 18 captive hazel dormice ( Muscardinus avellanarius) were used to measure the longevity of fur clips on three different body positions; shoulder, side and rump, during the active season and over winter. The dormice were examined, photographed and their fur re-clipped on one side at regular intervals within the monthly monitoring period (April to November) of the UK National Dormouse Monitoring Programme. Significant variation in hair regrowth between individuals was found. There was a 71% chance of a patch clipped just once being visible the following month, but a 90% chance for patches that had been re-clipped at least once. On persistence of the first clip, there was no significant difference between age groups but the differences between sexes and body positions were almost significant. Patches re-clipped in autumn could all be detected in spring, post hibernation.