BLACK BEARDED SAKI
Geographic Distribution and Habitat
The black bearded saki (Chiropotes satanas) is one of five species of bearded sakis living in the Amazon rainforest. Bearded sakis are commonly known in Brazil as cuxiú, a term long used by indigenous peoples to describe this particular genus of monkeys. Some researchers believe that the name cuxiú should replace the “bearded saki” moniker altogether, which they argue encourages a false association between bearded sakis, of the Chiropotes genus, and saki monkeys, of the genus Pithecia—a consistent source of confusion in both scientific and lay communities.
Today, black bearded sakis—or black cuxiú, as they may one day be known—are restricted to a small region of Brazil near the Tocantin River. This species prefers primary tropical rainforest where lush canopies offer a relatively safe zone out of sight, and beyond the reach of many predators.
Size, Weight, and Lifespan
The average male black bearded saki ranges in length from 13 to 19 inches (327–480 mm) and weighs in at a little over 6 pounds (3 kg). Females are only slightly smaller, ranging 12–18 inches (320–463 mm) in length and weighing, on average, just under 6 pounds (2.6 kg).
Though the average lifespan of black bearded sakis is unknown, closely related species have been found to live up to 20 years.
Black bearded sakis are primarily black in color, though some individuals have fur that is browner in hue. Males and females alike are most prominently distinguished by two rounded bulbs that protrude from their foreheads. Another conspicuous feature is their signature beards. Forehead and beard give them a well-rounded, heart-shaped profile. Their bodies are somewhat slender but defined, covered in an even matt of fur. From far off, their striking proportions and long bushy tails can make it hard to tell their heads from their rear ends.
Black bearded sakis have shorter forelimbs than hind limbs, and small, not fully opposable thumbs—features that are perfect for scurrying through the canopy. A more inconspicuous trait, but still significant, is their uniquely powerful jaws and specialized molars. These are optimal for chewing through thick, tough husks of unripe fruit to get at the nutrient-rich seeds inside.
Black bearded sakis are primarily granivorous, meaning they eat seeds. Strong jaws and specialized teeth give them the strength and integrity to rip through the tough outer layers of unripe fruit to get at the nutritious seeds inside. Black bearded sakis spend at least 75% of their annual feeding time just eating seeds and consume the seeds of more than 50 different fruits. They are some of the most efficient seed predators of their order.
Though they clearly show such a strong preference for seeds, black bearded sakis are actually quite flexible eaters. They adapt their diet throughout the year, depending on what is seasonably available. When seeds are hard to find, or if they require other nutrients, black bearded sakis may eat fruits, flowers, leaf stalks, and arthropods such as caterpillars, termites, and gall wasps. Sometimes, but very rarely, they have been observed to eat certain leaves.
Geophagy—or the ingestion of earth, soil, or clay—has also been observed in this species, albeit infrequently. Although swallowed by accident while the subjects were eating termites, some researchers hypothesize that ingesting certain minerals this way may help black bearded sakis absorb and process otherwise harmful toxins typically found in the seeds they consume at such high volumes.
Behavior and Lifestyle
A black bearded saki is arboreal, spending most of his time high up in the canopy. He scuttles from tree to tree on all fours, leaping and climbing only when a gap in the foliage makes it truly necessary.
Much of his daily activity is divided between finding food and eating the food that he finds. Trees with immature fruit offer him a feast inaccessible to the other (strictly frugivorous) primates of the jungle who must wait for the fruit to fully ripen. Upon finding such a tree, he and his troop chow down. Their strong jaws and wedge-shaped canines make easy work of the immature fruits’ thick shells, tearing through them to reach the seeds inside.
Fruit hanging out of reach, gives a black bearded saki no pause. Though her tail is not fully prehensile, she may drape it over a branch for extra support while she leans out. If the fruit is more than a little ways off, she can suspend herself for short periods of time by just her hindlimbs, extending her reach long enough to retrieve it. Fruit in hand, she reassumes a quadrupedal position (on all fours) to feed. She bites a hole into the husk with her specialized back teeth. Then, she uses her powerful incisors to pop off the seeds’ protective casing.
As a predator, the caterpillars she hunts prove no match for her keen eyesight and agility in the trees. Termite mounds and gall wasp nests are practically defenseless against her nimble fingers with which she extracts their meaty inhabitants and larva with ease. With ants she rests her arm near an active colony. When enough ants have climbed aboard, she picks them out of her fur and pops them into her mouth.
The term Chiropotes means “hand drinker”—a behavior once believed to be unique to this genus, but that is no longer the case.
Black bearded sakis eat one of the highest animal monthly percentages of seeds of any primate. Young black bearded sakis have been observed playing with young saki and howler monkeys in the wild.
A black bearded saki wakes at sunrise. During the night, his small troop slept comfortably and safe, tails wrapped around each other, in the branches of a tall tree. Now, another busy day of foraging begins.
His is one of several small black bearded saki troops in the area that make up a larger social group of up to 40 or so monkeys. Though members of this larger group remain bonded, they split into smaller bands while foraging, a social dynamic called fission-fusion. These smaller fusion groups may spend several days separated before rejoining one another.
Black bearded sakis forage somewhat ruthlessly. They move from one feeding spot to the next so quickly that they sometimes leave an individual behind. Deprived of his social support system, a black bearded saki becomes exceptionally vulnerable. It may be days, sometimes weeks, before he returns to the safety of his own troop. In the meantime, desperate for the security that being around others provides, he joins whatever group of sympathetic monkeys he may find, including those of other species. Indeed, spider monkeys, squirrel monkeys, and capuchins are all primates with whom black bearded sakis are known to occasionally fraternize.
Black bearded sakis spend at least 75% of their day traveling, making only brief stops to forage. Around midday, however, they may take a longer pause to rest. During such a break, the monkeys nap and socialize. High up in the canopy, beyond the reach of predators, relaxation comes naturally. Adults take turns grooming one another and juveniles play.
Groups of black bearded sakis are composed of multiple males and females. Relationships remain affable overall, but their social operations are not yet understood. Males do show a great deal more camaraderie with each other than females. For instance, adult males regularly take turns grooming their male and female peers, while adult females never groom other adult females, only juveniles.
Adult males are also known to huddle close together at times and make chirping sounds while wagging their tails in sync. Researchers believe this is a response to threatening situations, perhaps to scare off predators or to defend their resources and mates from rivals.
Shortly before sunset, a troop begins to wind down for the day. They find a tall tree, cuddle close together, and fall asleep.
Black bearded sakis use both vocalizations and body language to communicate.
Sound is a convenient way to keep in touch when the dense foliage often prevents monkeys from keeping an eye on one another. By making high-pitched whistles throughout the day, members remain in regular contact with their troop.
While feeding, black bearded sakis sometimes make subtle chirping sounds that seem to convey a sense of satisfaction. If an individual is suddenly disturbed, however, she emits a shrill cry.
Purring is important aspect of black bearded sakis’ mating rituals. Females purr prior to coupling, and males during. This vocalization is also made by infants while nursing.
Black bearded sakis use their tails to express excitement, or to silently make contact with group members. Allogrooming (mutual grooming) is an important method of forging and maintaining social bonds.
The full complexity of black bearded saki communication methods is not well understood yet.
Little is known about the reproductive habits of black bearded sakis. Though they live in groups with multiple males and females, some research suggests that this species may form monogamous partnerships.
Births tend to occur at the same time each year, between December and January, when the rainy season initiates the fruiting of many trees whose seeds are staples in the black bearded sakis’ diet. Researchers speculate that gestation takes approximately 4–5 months and that infants are weaned and capable of locomotion at 3 months of life—but these estimates are based off research done on a captive bearded saki hybrid. There is currently little research on the reproduction process of black bearded sakis in the wild.
Researchers do know with some certainty that a mother births a single infant and that she acts as their baby’s primary caretaker, nursing and carrying him around.
Infant black bearded sakis are equipped with fully prehensile tails for the first two months of their life. Researchers are unsure why their tails eventually lose this ability.
The ecological role of black bearded sakis is not well studied. Though they have a penchant for seeds, they probably do not play a significant role in their dispersal since the seeds are often eaten before they are viable.
Seeds are not only an energy-rich resource, they are also available for longer periods and at higher proportions than any other food source, giving black bearded saki populations a healthy buffer against annual food shortages. Seeds become available before the fruit has even ripened, meaning the sakis can forage free of competition from other, strictly frugivorous primates like spider monkeys. In fact, their biggest competitors for this resource are not other primates, but birds such as macaws and parrots whose beaks are also capable of cracking open hard shells and nuts.
The foraging habits of black bearded sakis can adversely affect the amount of fruit available for other species to eat later in the season, when they would be ripe enough for these species to eat.
The black bearded saki is classified as Endangered by the International Union for Conservation of Nature (IUCN, 2020), appearing on the IUCN Red List of Threatened Species. This species is already considered extinct in much of its original range, and current populations are trending downward at alarming rates. The number of mature individuals may be fewer than 2,500.
Like many endangered primates throughout the world, the greatest threat to black bearded sakis is the loss of their natural habitat driven by human development. Large infrastructural projects like highways and the Tucurúi Dam have sacrificed large swaths of habitable land to human interests while smaller projects, like logging and agriculture, continue to fragment the scant pieces of habitat left over.
For primates like the black bearded saki who stay high in the canopy but who are not especially skilled leapers and climbers, forest fragmentation creates a host of problems. Climbing down out of the canopy, for instance, requires extra time and energy that these primates would otherwise spend performing more natural behaviors. Additionally, leaving the canopy makes them easier targets for predators, including human hunters. In fact, forest fragmentation likely increases the rate at which black bearded sakis are hunted by humans since preferred game animals also decrease in number due to loss of their own habitats.
Furthermore, isolation caused by fragmentation creates genetic bottlenecks. The harmful defects and increased vulnerability to diseases that these cause can gradually render each new generation less viable.
Without significant efforts to save the black bearded saki from extinction, this species will soon become extinct. Fortunately, there are efforts currently under way to turn this trend around.
The Pitheciine Action Group (PAG) is an organization directly involved in black bearded saki conservation efforts. With help from an international committee established by one of Brazil’s top federal environmental agencies, PAG are developing a Conservation Action Plan for the black bearded saki.
A number of areas, both protected and unprotected, exist where the presence of black bearded sakis is possible but not confirmed. Therefore, surveys and research into the effects of fragmentation on isolated black bearded saki populations are needed for any future conservation efforts to have meaningful effects.
Black bearded sakis have found an ally in Projeto Kaapori (Project Kaapori). The Ka’apori capuchin (Cebus kaapori) is another Critically Endangered primate species with essentially the same range as the black bearded saki. Projeto Kaapori’s primary mission is Ka’apori capuchin conservation. However, in doing their work, they have simultaneously collected data on all other primate species living in the Ka’apori capuchin’s range, including black bearded sakis. In so doing, they are contributing information that is crucial to the PAG’s Conservation Action Plan. Additionally, they are showing how research and conservation projects can be planned in the future to benefit these species jointly.
Hope for black bearded saki conservation lies in the future of the Gurupi Biological Reserve. This reserve is the last significant patch of forest where black bearded sakis are known to be living. It, plus the many Amerindian reservations that border it, currently offers wildlife an estimated one million hectares of relatively unfragmented and untouched forest. Founded in 1988, Gurupi falls under the IUCN protection category as a “strict reserve.” It is one of the last remnants of the Belém Center of Endemism and, as such, its preservation is significant for a number of flora and fauna endemic to this area. Human activity is, therefore, heavily restricted within this reserve.
Deforestation pressures from illegal activities continue to plague the Gurupi Biological Reserve, however. A third of the reserve’s forest has been lost to local ranchers, timber companies, and illegal land settlers since its founding. Today, federal agencies like the Primate Protection Center (Centro de Protectão de Primatas Brasileiros) and the Chico Mendes Institute for Biodiversity Conservation (Instituto Chico Mendes de Conservação da Biodiversidade) are working to solve these and other pressures that face Gurupi with mixed results so far.
In addition to these federal protections, Gurupi is also supported by the Amazon Region Protected Areas Program, a collaboration between governmental and non-governmental agencies working to expand protections for the Amazon rainforest in Brazil. Furthermore, a proposition to create a South Amazon Ecological Corridor would connect the Gurupi Biological Reserve to other protected areas in the country. If initiated, the ecological corridor would eventually link more than 30,000,000 hectares (78,000,000 acres) of rainforest.
No doubt, the protection of their habitat will have mounting positive effects for black bearded sakis living within the Gurupi Biological Reserve. In tandem with the PAG’s developing Conservation Action Plan, the future of the black bearded saki does not seem as bleak as it once did.
This species is listed under the Convention on International Trade in Endangered Species (CITES) Appendix II.
Written by Zachary Lussier, November 2020. Conservation status updated December 2020.