Wild bearded capuchin monkeys (Cebus libidinosus) living in dry woodland habitat in the state of Piauí, in northeastern Brazil, are currently being studied because of their ability to use tools. The study site is a Biological Reserve of about 250 ha managed by the Fundação BioBrasil. Dorothy Fragaszy (University of Georgia), Elisabetta Visalberghi (Istituto di Scienze e Tecnologie della Cognizione, Rome) and their colleagues from Brazil — Patrícia Izar and Eduardo Ottoni (both of the University of São Paulo) and Marino Gomes de Oliveira (Fundação BioBrasil, Lauro de Freitas, Bahia) — have documented the capuchins using stone hammers and anvils to crack open palm nuts (Fragaszy et al., 2004). In June 2004, while photographing this tool-using behavior in a troop of approximately 10 capuchins, I observed one of the monkeys apparently caring for and feeding a common marmoset (Callithrix jacchus). The capuchin held the marmoset in its arms and let the marmoset cling to its chest and ride on its back (Fig. 1). At one point the capuchin (with the marmoset on its back) cracked open a palm nut using a stone hammer and anvil, repositioned the marmoset into its arms and then took small pieces of the cracked nut and gave these to the marmoset to eat. During the two hours of observation the marmoset stayed with the capuchin, either clinging to its chest or riding on its back, both while the capuchin was on the ground and when the capuchin climbed about 20 feet into the trees near where the capuchins were feeding. There was, however, one instance when the marmoset jumped off the capuchin and scampered about on the ground among the other capuchins in the troop. After about five minutes the caretaker capuchin went over to the marmoset and placed the marmoset onto its back.

Figure 1.

A wild bearded capuchin monkey (Cebus libidinosus) caring for and feeding a common marmoset (Callithrix jacchus).

The local residents were questioned concerning the marmoset and its association with the capuchin. They said that the marmoset suddenly appeared with the troop of capuchins and was seen for the first time about when these photographs were taken. What is certain is that the marmoset is not a pet or tame. It is also known that this species of marmoset lives in the wild in the same habitat as the capuchins. In September 2004 the local residents reported that the marmoset was still with the capuchin group, an association lasting at least 15 weeks thus far. These observations are believed to be unique (D. M. Fragaszy, pers. comm.). While interspecies play is sometimes observed in captive animals, interspecies carriage and feeding in wild populations is not.