Observed case of infanticide committed by a resident male central American black howler monkey (Alouatta pigra)

Although infanticide has been witnessed in other species of howler monkey, and has been inferred for Alouatta pigra, an observed case of infanticide has not previously been recorded for this species. Here we describe the killing of a 2-week-old infant by the resident male of a small social group in southern Belize. The infanticide was witnessed as part of an intensive observational study that began in January 2003. The male was known to have resided in the group for at least 4 months, but it is not known whether he was the father of the infant. The literature proposes three main explanations for infanticide: two adaptive hypotheses (sexual selection and resource competition), and one nonadaptive hypothesis (social pathology). Individual cases of infanticide such as this one are important for comparative purposes, but when examined on their own they are difficult to interpret in relation to established theoretical frameworks. The data presented here show some consistency with the sexual-selection and resource-competition hypotheses, but the lack of critical information (i.e., as to paternity) makes it impossible to draw firm conclusions.