Male adoption in the black and gold howler monkey (Alouatta caraya).

Infant adoption is an association that occurs between an adult individual and a dependent infant and occurs most often when lactating females care for a nutritionally dependent infant that is not her offspring. Adult females are often involved in adoption; while, direct infant care by males occurs in less than 5% of all mammalian species. We report the first record of adoption by wild male adults of Alouatta caraya, a platyrrhine primate species that does not typically participate in parental care. We observed two independent cases of adoption, in two different groups (G1, G2) at the Corrientes Biological Station, Argentina. After the death of two adult females with dependent infants, one adult male adopted an orphan in each group. We recorded the activity of the adoptive males and the two infants. During this period, adoptive males expressed parental care behaviors toward infants. However, after 38 days in G1 and 53 days in G2, both infants died. Based on our continuous monitoring of study groups, we suggest that adoptive males are the biological parents of the orphaned infants. As such, kin selection may explain the care of the infants. However, another explanation could be group familiarity, which refers to the social bonds and cohesion that develop among individuals within a group, even if they are not genetically related. An adult male, although not genetically related to the infants, may take care of them due to the cohesion and relationships established within the group during his period of residence. The study of these rare parental behaviors taken by A. caraya adult males provide insights into the knowledge of group social cohesion and structure.