Infanticide in the meadow vole, Microtus pennsylvanicus: Significance in relation to social system and population cycling

The relationship between social experience and readiness to commit infanticide was investigated in male meadow voles, Microtus pennsylvanicus. Shortly after a female gave birth, either the male (stud) that had sired the litter, a strange male that had had recent contact with a sexually mature female, or a strange male that had not had recent contact with a sexually mature female was placed in her cage for 24 hr. Tendency to commit infanticide was least in stud males, greatest in strange males that had no recent contact with sexually mature females, and intermediate in strange males that had recent contact with sexually mature females. Length of gestation in females impregnated by strange males was about 1.5 days longer when lactating than when not lactating. There was no difference between length of gestation of lactating females impregnated by stud males and those impregnated by strange males. Infanticide apears to be a reproductive tactic of male meadow voles, and, in conjunction with pregnancy failure in females, may have a significant influence on population regulation in this species. Dispersal may affect population cycles through the occurrence of infanticide and pregnancy failure when strange individuals immigrate into resident populations.