Black-capped capuchins (Cebus apella) are known to feed on a wide variety of vertebrate prey, including lizards, frogs, birds, bats, marsupials, rodents, and squirrels (Izawa, 1978, 1990; Terborgh, 1983; Galetti, 1990; Rímoli, 2001; Resende et al., 2003; Defler, 2004), although to date, there is only one report involving another primate, an infant titi, Callicebus moloch (Sampaio & Ferrari, 2005). Here we describe the behavior of a group of black-capped capuchins feeding on an adult female owl monkey (Aotus brumbacki) in a fragment of gallery forest in the Colombian Llanos. This appeared to be the scavenging of a carcass, rather than a predation event, but the observation nevertheless emphasizes the potential of the capuchins for the exploitation of prey this size.

The event was recorded during the long-term monitoring (September 2005 to January 2007) of a group of 43 squirrel monkeys, Saimiri sciureus albigena (Carretero-Pinzón, 2008) on the Arrayanes Farm (3°3′30″N, 73°35′40″W) near San Martin in the Colombian Llanos, department of Meta (Fig. 1). The group occupied a matrix of small fragments of gallery forest of up to 21 ha, including those on the neighboring Santa Rosa Farm, that are interconnected by fences. We collected quantitative behavioral data in scan samples (one minute scans at five minute intervals), and whenever an association was formed with the local group of Cebus apella [during 28.3% of monitoring time (1,113 hours of total observation time)]. We also collected data on the members of this group (1 adult male, 1 adult female, 2 juveniles, and 1 infant) using the same sampling schedule. During the event reported here we abandoned this schedule and the capuchins were monitored continuously for the first half hour and then at five-minute intervals, until the carcass was abandoned.

On the morning of January the 12th, 2006, when the squirrel monkeys and capuchins were foraging together in a mixed troop at approximately 08:35, the adult male C. apella apparently found a dead female owl monkey (Aotus brumbacki) in a tree hole. The assumption that the capuchin found the owl monkey rather than captured it alive is based on the lack of visible or audible evidence of hunting activity or prey capture. On finding the carcass, the adult male became visibly excited, and emitted feeding vocalizations, that were answered in kind by the four other group members, who then approached to a distance of 3–5 m from the tree-hole, from where they observed the male. The male pulled the owl monkey's legs out of the hole and began biting, tearing and eating the flesh of one of the legs. The male was the only individual to feed on the carcass during the first eight minutes, but then he moved to a neighboring tree to rest and looked on as the other group members moved in to feed. The adult female and the infant fed on the second leg; then one of the juveniles pulled the carcass out of the hole as far as its neck, bit off the right radius and hand, and ran to the neighboring tree to consume these parts. The four individuals each spent some 8–10 minutes feeding on different parts of the carcass. Tolerance and sharing appears to be typical of vertebrate predation in the capuchins (e.g. Perry and Rose, 1994; Resende et al., 2003), at least where relatively large-bodied prey is concerned (Izawa, 1978). After approximately 20 minutes, the adult male returned to feed on the carcass in close proximity with the infant, while vocalizing aggressively towards the female, who responded submissively and moved to a neighboring tree. The infant eventually joined the female to be groomed, and one juvenile rested nearby while the other foraged for arthropods. All five group members ingested parts of the owl monkey's limbs, tail or dorsal musculature, but, while one of the juveniles probed the abdomen with its hand, none of the capuchins appeared to feed on the intestines or internal organs. Curiously, Resende et al. (2003) recorded the opposite pattern in the predation of a rat by C. apella, where the soft parts were consumed and the musculature ignored. In the present case, the freshness of the carcass was possibly a factor —the time of death was not known, but presumably preceded the scavenging by at least a few hours. After approximately one hour of intermittent feeding and resting, the capuchins abandoned the carcass as vultures began to arrive at the scene. The remains of the owl monkey's body — the skeleton and some fragments of skin — were found at the same location two days later. The capuchins moved through this area in the interim, but they did not approach the carcass.

Figure 1.

Location of the study area, showing the main fragments of gallery forest on the Arrayanes (16 ha) and Santa Rosa (21 ha) farms in the Colombian Llanos.

Capuchins are highly resourceful and opportunistic primates, able to exploit a wide variety of foods, so in this sense, the events observed here were well within the behavioral potential of the species. As it appears that the body of the owl monkey was scavenged, rather than captured alive, it still remains unclear whether capuchins would normally, if ever, prey on adult primates the size of Aotus, which have a body weight of approximately 1 kg. The only record of a capuchin predation of another primate involved an infant titi (Sampaio and Ferrari, 2005), and predation of terrestrial mammals by capuchins has involved either small-bodied rodents or the infants of larger-bodied species, such as coatis and opossums (Newcomer and De Farcy, 1985; Rose and Perry, 1994; Resende et al., 2003; Fragaszy et al., 2004). In this context, it is interesting to note that Saimiri, which associates systematically with Cebus during foraging at many sites - including the present one — is actually slightly smaller than both Aotus and Callicebus. Even so, there appear to be no reports of capuchins actively pursuing or preying on squirrel monkeys, even juveniles. In addition to other factors, in the specific case of Saimiri, the potential benefits of predation may be more than out-weighed by those of the foraging association (Terborgh, 1983; Boinski, 1996).