Stay Gathered Rather than Scattered: Strategies of Common Marmosets during Agonistic Interactions with Birds in the Atlantic Rain Forest.

To reduce the vulnerability of their small body size, common marmosets live in large and cohesive social groups. Thus, we hypothesized that in order to compensate for small body size and predation risk, individuals of common marmosets will stay gathered rather than scattered when foraging for eggs and/or nestling birds. Furthermore, in order to avoid costly injuries and eventual predation risks, for both sides, the majority of interactions among common marmosets and small birds will not involve direct physical contact. The study was developed in a small fragment of Atlantic Forest in the northeast of Brazil. We recorded a total of 115 interactions between common marmosets (Callithrix jacchus) with 7 different bird species. As expected, agonistic interactions were significantly more frequent when the marmosets were gathered. Also, most agonistic interactions by the birds toward common marmosets involved overflights without physical contact. Apparently, the set of avoidance behavior leads to a reduced predation risk for both sides. It appears that dispersed marmosets do not represent an imminent threat that justifies an agonistic reaction by the birds as the latter appear to avoid exposing themselves to unnecessary danger during agonistic interactions, especially when the marmosets are gathered.