Geographic Distribution and Habitat
The bearded capuchin, also known as the black-striped capuchin, is found in northern and central Brazil. The species inhabits dry, deciduous forest and savanna landscapes. Its range is bordered by the Rio Araguaia to the east and the Rio Grande to the south. Unlike some other capuchin species, it is not found in the Amazon rainforest.
Size, Weight, and Lifespan
Adult males and females both have an average head and body length of 14.6 in (37 cm) but differ dramatically in weight, with males weighing on average 7.7 lb (3.5 kg) and females just 4.6 lb (2.1 kg). They also display sexual dimorphism in the length of their canines with males averaging 0.6 in (1.5 cm) and females just 0.4 in (1 cm). Body mass in males is related to social status; when males become alpha their body mass can increase by around 20%. When they lose their dominance status, they will also lose the extra body mass. Life expectancy in a wild bearded capuchin is thought to be approximately 20–25 years, although capuchins can live much longer in captivity.
Distinct differences in size or appearance between the sexes of an animal in addition to differences between the reproductive organs themselves.
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At first glance, bearded capuchins look very similar to other species of robust capuchins in the genus Sapajus. They have a mixed pelage that ranges from a yellow-gold to dark brown, with darker hair on their heads, their tails, and around their arms and legs. As they reach sexual maturity, they develop two small, dark tufts of hair on their heads and have dark “sideburns” running down the sides of their faces. Their faces can vary in darkness, but they tend to have lighter hair around their mouths and lower face, explaining why they are called “bearded capuchins.” They also have strong, prehensile tails from which they can hang and which they also use for balance.
They do have some features that distinguish them from other capuchins; the hair on their throats is orange and they have more of a yellow coloration to the dorsal parts of their body than other species.
Fruit makes up about 50% of the bearded capuchin’s diet, with invertebrates also making up a large proportion. They also consume other plant parts, such as flowers and leaves, to supplement their diet.
One aspect of the bearded capuchin’s diet has led to it becoming relatively famous among primatologists. Capuchins are the only non-ape primate to engage in nut-cracking behaviors. Bearded capuchins use stone tools to crack open the hard shells of palm nuts so that they can eat the kernel within. To do this they place the nut on a boulder or hard surface (an “anvil”), then lift up a stone (a “hammer”) with both hands and then smash it on top of the nut in order to break the shell. They often stand bipedally (on two legs) while nut cracking and strategically place the nuts on the anvil in such a way that they have the best chance of cracking the shell.
Behavior and Lifestyle
Bearded capuchins are diurnal—most active during daylight hours—and spend the nights sleeping in trees. During the day they spend a large proportion of their time foraging and traveling, especially during the dry season when less fruit is available. Compared to capuchins who live in rainforests, these savanna-dwelling capuchins spend a higher proportion of their time on the ground. They generally move quadrupedally (on all fours), however, they are also known to walk bipedally when carrying heavy rocks in both arms for nut cracking. In this case, they use their thick tails for balance.
Adults of both sexes show a high level of tolerance toward young individuals, allowing them to observe nut cracking from close range and even allowing them to take cracked pieces of nuts from their hands. Young capuchins take several years to learn how to crack nuts and this high level of tolerance and associated scrounging likely helps them to learn this skill. This social learning allows nut-cracking skills to be passed on through generations and likely forms the evolutionary basis of the cultures that we see in humans.
This species has even been known to “adopt” an infant of another monkey species, an incredibly rare behavior among primates.
Bearded capuchins are one of very few species of primates to engage in nut-cracking behaviors.
When females wish to mate with a male, they follow him around and sometimes even throw rocks at him.
Bearded capuchins live in mixed-sex groups. Group sizes can range from 8 to 20 individuals and are very cohesive. Females are philopatric and remain in the group where they were born, while males migrate to a new group. Groups generally contain more females than males, often with a ratio of approximately two females for every male. Males form linear dominance hierarchies with an alpha male who is dominant over all members of the group. The alpha male is central to the social network of the group and females show a preference for grooming him, although they will also groom each other. Females also establish linear dominance hierarchies and form coalitions with other females during conflicts. Unlike the alpha male, subordinate males are often found on the periphery of the group.
Bearded capuchins communicate using a wide variety of facial expressions, including scalp-lifting, lip-smacking, and the open mouth threat face. Facial expressions are used during courtship rituals but also during other affiliative and aggressive encounters along with gestures, vocalizations, and body postures. These capuchins emit a number of vocalizations, including alarm calls when they see predators, such as birds, snakes, or dogs.
Bearded capuchins engage in a number of interesting and unusual courtship rituals. When females are ready to mate, they follow a male around trying to attract his attention. This can even involve the females throwing rocks or sticks at the male. The male initially tends to be either disinterested or aggressive toward the female. This is followed by “touch-and-run” behaviors whereby females touch a male and then run away before he can direct aggression at her. Eventually the male reciprocates the female’s interest and they are able to mate.
Females generally try to solicit the alpha male’s attention and the alpha male fathers the majority of the group’s infants.
Females reach sexual maturity at around five years of age and give birth approximately once every two years, usually to a single infant. Infants are carried on their mother’s belly initially and are later carried on her back. Infants are weaned gradually but forage independently by two years of age. Males are often classed as adults at around five years of age but do not reach an average adult mass until they are around ten years of age.
Bearded capuchins have a diet that is high in fruit and therefore likely play an important role in the ecosystem via seed dispersal.
The bearded capuchin is currently classified as Near Threatened by the International Union for Conservation of Nature (IUCN, 2015). The population is declining and accurate estimates of population density are not available.
Although the bearded capuchin remains remains widespread in some biomes in Brazil, fifty percent of their habitat has been deforested. As their habitat is modified for agriculture, some monkeys resort to raiding crops for sustenance, resulting in persecution by farmers. As great as those threats are, greater still is the severity of hunting and collection of bearded capuchins from the wild for the illegal pet trade.
The seriousness of the hunting pressure is demonstrated by the high number of individuals seized from illegal trade by the Wild Animal Screening Centers. Most of these seized individuals cannot return to the wild because of physical and behavioral disorders caused in captivity. Additional threats are hybrids or exotics deliberately released from captivity.
The bearded capuchin is currently listed under the Convention on International Trade in Endangered Species (CITES) Appendix II, meaning that trade in this species is subject to international controls. Although it inhabits some protected areas, more research into the population density and trends is needed.
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Written by Jennifer Botting, December 2019