American Journal of Primatology 68:692–700 (2006) RESEARCH ARTICLE Cross-Genus Adoption of a Marmoset (Callithrix jacchus) by Wild Capuchin Monkeys (Cebus libidinosus):

We report a case of interspecies adoption of an infant marmoset (Callithrix jacchus) by wild capuchin monkeys (Cebus libidinosus). The marmoset was an infant when it was first observed in the capuchin group on 3 March 2004. Since it first appeared it has been observed informally and frequently. In January 2005 systematic observations were made of the marmoset and a capuchin of similar age. Throughout its period of adoption the marmoset appeared to be socially integrated into the group, benefiting from nurturant behaviors exhibited by two successive adoptive ‘‘mothers’ ’ and pronounced tolerance from all members of the group. This case highlights the flexibility of both Callithrix and Cebus in accommodating variable social behaviors and other characteristics (including size) of social partners. Am. J. Primatol. 68:692–700, 2006. c 2006 Wiley-Liss, Inc. Key words: adoption; Cebus; Callithrix; maternal behavior; developmen