These agile and fast-moving monkeys are often detected because of debris falling from the treetops as the monkeys rip apart fruit clusters and bark to forage for insects and sweet ripe fruit morsels. They forage at all levels of the forest, feeding on a great variety of foods, mainly ripe fruits and invertebrates, but also an occasional lizard, frog, snake, birds’ egg, baby squirrel or bird, or even a nestling coati. They have been observed stalking and lunging at adult squirrels and tamarins. Capuchins can be seen in the late afternoon around the residence buildings, feeding on the nectar of balsa flowers. Dr. Betsy Mitchell observed capuchins feeding on 116 species of plants during a two-year study. When combined with a study by the Hladiks, also on BCI, the number of food species totals 169. Capuchins use another 8 species of plants to rub into their fur, perhaps to condition their skin or to repel parasites.
Visitors to BCI are often surprised to see these monkeys walk upright on two legs on the forest floor. They easily use all levels of the forest. Capuchins are very vocal, giving out barks, whistles, and screams as they move, calling to each other to maintain contact. Deer, coatis, and agoutis take advantage of the falling food under trees where a large group of capuchins is feeding. Visitors can usually find a troop to observe and will often see species that associate with capuchins. Pairs of double-toothed kites, which are small, very elegant predatory birds, move through the forest with the monkeys in order to capture lizards and insects as they flee from the capuchins. Capuchins express their dislike for being observed by humans by shaking vines and branches and pushing loose twigs, leaves, and even very large branches, out of the treetops. Their distinctive, recognizable faces and individual personalities make capuchins particularly interesting to observe. They have the largest brains, relative to body size, of all the New World monkeys, and are known for their intelligence.
The species of capuchin on BCI, the white-throated capuchin (Cebus capucinus) has black upperparts with whitish neck, shoulders and upper arms. The head is yellowish with a black cap; the face is pinkish. The long black tail is used for grasping, but not as extensively as in spider monkeys. As they walk along branches, they usually carry the tail coiled underneath at the tip, which gives rise to one common name, “Ringtail.” Adults weigh 2 – 4 kg, with males heavier than females. The species ranges from Honduras to northern Ecuador. In Panama they are called cariblanca.
Capuchins are an extremely social species that lives in groups averaging about fifteen, and ranging from 2 to 24. Usually two adult males, 4-8 adult females, 1-2 subadult males, 5-9 juveniles, and up to 5 infants may be present in a troop on BCI. There were 18 groups recorded on BCI in 1966, when Oppenheimer was studying their biology; in 1987, Mitchell recorded 16 groups plus a possibility of two others. She estimated 278-313 capuchins on BCI, while Oppenheimer estimated 270 from his 1966 data. This suggests that the population has increased slightly but is fairly stable over the long-term.
Young capuchins usually stay with their group for the first four years of life, sometimes emigrating as they approach maturity. Emigration of older adults to another group, however, seems to be an unusual occurrence. Young are born most often from February to May. The gestation period is 5 months and a female usually has only one young in two years. Mothers may nurse a baby for two years, during which time they usually do not become pregnant again. Young start feeding independently at about 4 months of age. Subadults and juveniles share in carrying infants after 3 months of age. The first two years of a capuchin’s life are the most dangerous, and mortality is highest at this time. If a capuchin lives to adulthood, it has an excellent chance of living a long life.
A group uses 77-110 h of forest in its daily wanderings, moving 1.5 to 3.5 km each day. During the season of fruit scarcity on BCI, capuchins feed on a great diversity of small fruits that are usually thought of as bird fruits. They may also feed on a greater proportion of insects at this time. Mitchell’s work on foraging behavior showed that capuchins use different patterns of foraging in different seasons. The season when young are ready to start feeding on their own is the time when many small, easy-to-handle fruits are ripening. These are also fruits that are found in short trees that are easy for a young monkey to enter. Large trees are barriers to the young, who must wait to be carried into tall trees by an experienced adult. The movements of groups with young that are learning how to forage are more restricted than in groups with tiny portable infants or weaned youngsters. The group restricts both its horizontal and its vertical movements to accommodate the limited climbing skills of the young. The timing of births permits the weaning stage to coincide with the season of small fruits. This timing is thought to be an adaptation to enhance survival of the most vulnerable individuals. Similarly, the peak of births in the BCI population coincides with the availability of large patches of food that allow mothers to feed well and rest frequently. In any season, individuals adjust their behavior to different distributions of food resources in order to also maintain the integrity of the social group.
The home ranges of different groups are broadly overlapping, so groups often meet. When groups meet, they chase each other and shriek. Adult males appear to be dominant over adult females, but the full story is probably much more complex. Adult males defend the group from other monkey groups and from predators, and females often participate in the chase. The predators of capuchins on BCI are probably boa constrictors, ocelots, and tayras. Historically, harpy eagles preyed on monkeys in Panama. Capuchins on BCI have been observed to mob and call loudly when they detect tayras, hawks, caimans, and boas.
J. Giacalone and B. J. Mitchell, 1977