Behaviour of cyclic bank voles under risk of mustelid predation: do females avoid copulations?

Mustelid odours have been shown to suppress breeding in captive bank voles (Clethrionomys glareolus) from cyclic populations (Ylönen 1989; Ylönen and Ronkainen 1994). The mechanism behind the suppression is unknown. Based on a series of behavioural trials and breeding experiments with pairs of bank voles in breeding condition, we suggest that the primary cause for breeding suppression is a change in female mating behaviour. Experimental female-male pairs (n=34) exposed to mustelid odour decreased their general activity compared to control pairs (n=34). When encountering males in behavioural trials, females exposed to stoat odour were more aggressive and actively avoided precopulatory behaviours of males. No copulations were observed in experimental pairs compared to five in control pairs during the behavioural trials. Males actively approached females in general but male behaviour did not change under exposure to mustelid odours. We suggest that females are more vulnerable to mustelid predators than males and therefore actively avoid copulations in the (indirect) presence of mustelids. As well as this behavioural response, internal abortive mechanisms (cf. Bruce 1959) could play a role in the observed breeding suppression.