GRAY'S BALD-FACED SAKI
Geographic Distribution and Habitat
Gray’s bald-faced sakis, also known as the Rio Tapajós saki, are a species of saki monkeys found in the Amazon basin of South America. They inhabit areas of northeastern Brazil, in the states of Acre and Amazonia in the Amazon basin. Their range also extends into south-eastern Peru and the very north of Bolivia, and is bounded by major rivers which act as barriers to the dispersal of these monkeys. Their distribution across these areas appears patchy, but, due to their quiet nature and avoidance of humans, their populations can be hard to assess.
These sakis show a strong preference for closed-canopy, tropical moist forest compared to other local habitats such as palm swamps or floodplain forests, which they tend to use less. They also tend to avoid bamboo forests where possible.
Size, Weight, and Lifespan
Males and females of this species are fairly similar in size. Both male and female head and body lengths are, on average, 16 inches (41 cm). The tails of both sexes are approximately 18.3 inches (46.5 cm) in length and both sexes have canines around 0.35–0.39 inches (9–10 mm) in length.
Males tend to be heavier, weighing approximately 6 lb (2.7 kg) compared to an average female weight of 4.5 lb (20 kg).
Little is known of their life history, but similar species of monkeys generally live up to 30 years of age.
Gray’s bald-faced sakis are medium-sized monkeys with a memorable presence thanks to their distinctive pelage. Long dense hair gives a shaggy and unshorn appearance. Although their color reads as “grizzled” gray, their hair is actually black with long bands of white. There is some white hair above their dark brown eyes and light-colored hairs form distinctive “bangs” above the eyes. Their faces are unpigmented—appearing gray/pink in color—and get darker with age. As their names suggest, they have less hair on their faces than most other saki species.
Their hands and feet are covered in white hair, although their forearms tend to be brown and adult males have a distinctive orange ruff. Their tails are thick and hairy. These tails are non-prehensile, meaning they can’t be used to grip branches like the tails of spider monkeys or capuchins.
Coloration can vary with geographic region, with females in the Acre region often appearing lighter in color than females elsewhere.
Sakis are frugivores; their diet generally consists of over 90% fruit, although they also eat leaves, flowers, and insects. Gray’s bald-faced sakis show a specialized form of frugivory, because they feed primarily (over 80% of the time) on the seeds of unripe fruits. Since unripe fruits are more available than ripe fruits throughout the year, this allows them to maintain their diet even when ripe fruit availability is low—and also avoids competition with other fruit-eating animals. Their strong teeth help them to break into the unripe fruits and their diet includes over 200 different plant species.
Behavior and Lifestyle
Gray’s bald-faced saki monkeys are arboreal and diurnal primates; they sleep high in the trees at night and are active during daylight hours. They spend all their time in the trees and do not venture down to the forest floor. These sakis spend around 50% of their time foraging, with the remainder of the day spent resting, moving, or engaged in social activities, such as grooming and playing.
While they tend to ignore smaller species of primates with whom they share habitat, they will go out of their way to avoid larger or more aggressive primate species, such as spider monkeys or capuchins.
Gray’s bald-faced sakis have a distinctive line of hair above their eyes, giving the impression of “bangs.”
These monkeys have a reputation for being reclusive, due to their quiet nature and their avoidance of humans.
They display a specific type of frugivory by feeding primarily on the seeds of unripe fruits.
Daily Life and Group Dynamics
Groups are generally small, usually in the range of 2–8 individuals. These groups usually contain one adult male and between one and three adult females, as well as juveniles and infants. These sakis likely have a flexible social system, including both single-pair mating and polygyny.
The home ranges of different groups often overlap with one another and although interactions between groups are not frequent, they are usually agonistic. These agonistic intergroup interactions tend to take place in preferred habitat areas, suggesting that there is competition between groups for these areas.
Gray’s bald-faced sakis have earned the reputation of being quiet and reclusive monkeys; they do not use loud vocalizations as much as some other forest-dwelling primates. However, saki monkeys can emit loud and prolonged alarm calls when they spot a terrestrial predator approaching. This can warn the rest of the group of imminent danger. While little is known about the other vocalizations produced by the species, other species of saki monkeys are known to emit squeaks, whistles, and trills, as well as barks, grunts, and roars, which can be used in more agonistic contexts.
It is also likely that they utilize olfactory communication; other saki monkey species are known to use both urine and secretions from glands in their neck to scent-mark their territory.
Reproduction and Family
Not many details are known about the reproductive habits of the Gray’s bald-faced sakis, but it is likely that mating can occur throughout the year and that, after a gestation of approximately 150–180 days, a single infant is born. The infant clings to his mother’s front when he is a newborn, then moves to her back as he gets older. Sexual maturity probably occurs at around three years of age and individuals may then leave the family group to find their own mate.
Seeds make up a large part of this species’ diet and therefore it is likely that they have an important impact on seed dispersal throughout their home range by carrying ingested seeds far from their parent tree.
Predators of the Gray’s bald-faced saki monkeys include Harpy eagles, as well as terrestrial predators such as jaguars.
The Gray’s bald-faced saki monkeys’ conservation status is currently listed on the International Union for Conservation of Nature’s Red List of Threatened Species as Data Deficient (IUCN, 2015), meaning that researchers do not know enough about its population to know if it is threatened. Despite this, the overall population is expected to be in decline.
Threats to this species include habitat loss due to deforestation and hunting. It is hunted for the pet trade and sometimes to use its distinctive pelage as decoration.
Trade in sakis is subject to some international regulation and some of the population occurs within protected areas. However, more research on this species is desperately needed into order to accurately assess population numbers and trends and to identify specific threats to its conservation. Once more details are known, more effective conservation actions can be put in place.
- Adams, D. B., & Kitchen, D. M. (2018). Experimental evidence that titi and saki monkey alarm calls deter an ambush predator. Animal behaviour, 145, 141-147.
- Palminteri, S., & Peres, C. A. (2012). Habitat selection and use of space by bald-faced sakis (Pithecia irrorata) in southwestern Amazonia: lessons from a multiyear, multigroup study. International Journal of Primatology, 33(2), 401-417.
- Palminteri, S. (2010). Determinants of primate distribution and abundance in south-western Amazonia, with a focus on bald-faced saki monkeys (Pithecia irrorata) (Doctoral dissertation, University of East Anglia).
- Marroig, G., & Cheverud, J. M. (2004). Cranial evolution in sakis (Pithecia, Platyrrhini) I: interspecific differentiation and allometric patterns. American Journal of Physical Anthropology: The Official Publication of the American Association of Physical Anthropologists, 125(3), 266-278.
- Marsh, L.K., 2014, Journal Article.A Taxonomic Revision of the Saki Monkeys Pithecia Desmarest 1804. Neotropical Primates 1-163.
Written by Jennifer Botting, PhD, May 2020