Forcible snatching and probable killing of infants by a rhesus (Macaca mulatta) alpha male in a wild habitat

Abstract

The alpha male of a group of 11 rhesus monkeys living in a forest became infanticidal after the removal of all of his group members. His ranging activity and protective behavior decreased while his aggressive behavior increased. He started visiting 6 mother-infant pairs that were placed in the study area for some other experimental purposes. Five infants were forcibly snatched from their mothers and were probably killed; in the sixth case, the mother managed to escape with her infant. However, the alpha male resumed his normal activity after the introduction of 6 new females. It is suggested that a threat to the male's individual fitness was the major reason for his infanticidal behavior. A hypothesis is proposed to explain the phenomenon of infanticide in nonhuman primates.