BEHAVIOR OF CYCLIC BANK VOLES UNDER RISK OF MUSTELID PREDATION - DO FEMALES AVOID COPULATIONS

Mustelid odours have been shown to suppress breeding in captive bank v oles (Clethrionomys glareolus) from cyclic populations (Ylonen 1989; Y lonen and Ronkainen 1994). The mechanism behind the suppression is unk nown. Based on a series of behavioural trials and breeding experiments with pairs of bank voles in breeding condition, we suggest that the p rimary cause for breeding suppression is a change in female mating beh aviour. Experimental female-male pairs (n = 34) exposed to mustelid od our decreased their general activity compared to control pairs (n = 34 ). When encountering males in behavioural trials, females exposed to s toat odour were more aggressive and actively avoided precopulatory beh aviours of males. No copulations were observed in experimental pairs c ompared to five in control pairs during the behavioural trials. Males actively approached females in general but male behaviour did not chan ge under exposure to mustelid odours. We suggest that females are more vulnerable to mustelid predators than males and therefore actively av oid copulations in the (indirect ) presence of mustelids. As well as t his behavioural response, internal abortive mechanisms (d Bruce 1959) could play a role in the observed breeding suppression.