Observed infanticides following a male immigration event in black howler monkeys, Alouatta pigra, at Palenque National Park, Mexico.

This study describes two cases of directly observed and one case of nearly observed infanticide after an adult male immigrated into a multimale-multifemale group of black howler monkeys (Alouatta pigra) at Palenque National Park, Mexico. The immigrant male entered the group alone, injured the central adult male, presumably evicted the noncentral adult male, and killed all three young infants present over the course of three consecutive days in February 2010. Three weeks after the infanticide events, the three adult females who lost their infants were observed to sexually solicit and copulate with both the infanticidal male and the injured central male. Multimale mating is an effective reproductive strategy that females employ to confuse paternity and reduce the risk of infanticide, but the extent to which promiscuous mating after infanticide events is part of a counterstrategy in this species is still unknown. More cases of infanticide will need to be observed to assess the degree to which infanticide avoidance shapes the social system of the black howler monkey.