Immigrating males often kill young infants when they take over a group. Females band together to defend their infants from infanticidal males, but they rarely succeed in saving their infants. Because infants inhibit their mothers from ovulating by nursing frequently, males are able to bring females into estrus earlier by killing the infants and thereby terminating nursing; this has the effect of increasing their breeding opportunities. Females do often mate with the killers of their infants, and with time, they typically become as supportive of the new alpha male as they had been of the previous one. The alpha male helps defend females from subordinate males within the group as well as from infanticidal males from other groups.