Infanticide in the bank vole (Clethrionomys glareolus): Occurrence and the effect of familiarity on female infanticide

Abstract

We studied infanticide in the bank vole (Clethrionomys glareolus), in a species whose social organization is characterized by strict female territoriality during the breeding season. One possible origin of female territoriality could be to protect the nest site and pups from potentially infanticidal conspecifics. However, direct evidence of the occurrence of infanticide, and thus of its possible role in territorial behaviour of the bank vole females, is totally lacking. Observations in the laboratory, but also in the field and small enclosures yielded a proportion of 30% or more of infanticidal cases of both females and males intruding a strange nest. If an individual of either sex was infanticidal it killed all the pups in the nest. In 36 trials in eight 25-m(2) enclosures we tested the occurrence of infanticidal behaviour in voles from three female categories: mutually familiar females with neighbouring "territories" and mutually unfamiliar "stranger" females either breeding or non-breeding. In "stranger" females the proportion of infanticidal individuals was 25% in non-breeding and 42% in breeding ones. Mutual familiarity between neighbours decreased the frequency of infanticide significantly to only 6%. In a control group of adult non-familiar males the proportion of infanticide individuals was 67%. Thus, both sexual selection (males) and resource competitions (females) infanticide was observed for the first time in the bank vole or in general in Clethrionomys spp. Territoriality in the bank vole may function to deter potentially infanticide intruders from entering the nesting area and killing pups. It might be that in a breeding system of philopatric females, mutual familiarity between neighbouring females would decrease the frequency of infanticide. This would be reflected in higher survival of young in a breeding population of philopatric females with a high degree of kinship and/or familiarity.