Gray’s Bald-Faced Saki, Pithecia irrorata
GRAY'S BALD-FACED SAKI
Pithecia irrorata
Geographic Distribution and Habitat
Mostly occurring in protected areas of Peru, the Gray’s bald-faced saki (Pithecia irrorata) is an elusive primate native to the beautiful continent of South America.
The Gray’s bald-faced saki, has a home range that stretches from northern and central South America, touching northern Bolivia, and into central parts of Brazil. In Brazil, the Gray’s bald-faced saki’s geographic range follows the west side of the Rio Purus south to Acre. In Peru, this primate occurs west of the Rio Manu and south of the upper Rio Madre de Dios.
Because of their large geographic distribution, they are able to live in a wide range of forest types. These forest types include flooded forests (white-water flooded forests), igapó (black-water flooded forests), palm swamps, and terra firma forests.
Although there is not much research to prove their forest type preference, most evidence suggests that they prefer to live in tall, unflooded forests. Considering these characteristics, terra firma forests appear to be best suited for the Gray’s bald-faced saki. As they prefer to live in elevations of up to 656 feet (200 meters), these forests are typically very thick and are home to several different mature plant species.
In the world of taxonomy, the classification of saki monkeys is considered difficult, specifically due to the misuse of names, lack of data, and imprecise locality studies.
J. E. Gray first discovered the Gray’s bald-faced saki in 1860. After reviewing Geoffroy Saint-Hilaire’s 1851 version of the Catalogue Méthodique de la Collection des Mammifères, a catalog of Mammalia specimens in Paris, France’s Natural Museum of Natural History, Gray recognized this monkey as a subspecies of Pithecia monachus, commonly referred to as the monk saki. According to Gray, Pithecia irrorata also had two different forms based on geography: Pithecia irrorata irrorata, the Gray’s bald-faced saki, and Pithecia irrorata vanzolinii, the Vanzolini’s bald-faced saki.
In 2014, through phenotyping and genetic testing, L.K. Marsh elevated the subspecies to a full species status, with the Gray’s bald-faced saki bearing the scientific name Pithecia irrorata and the Vanzolini’s bald-faced saki, Pithecia vanzolinii.
Size, Weight, and Lifespan
An adult Gray’s bald-faced saki typically weighs between 2.6 to 8.8 pounds (1.18 to 4 kilograms). Males tend to be heavier than females, leaning towards the higher end of the scale. The average body length of a saki is about 16 inches (40.64 centimeters). The average tail length, which can be as long as the body length, is around 18.3 inches (46.48 centimeters) long.
In captivity, the life expectancy of most animals tends to be longer than an animal’s life expectancy in the wild. Captive saki monkeys—with the benefit of regular meals, medical care, and no predators—may live between 20 to 30 years of age. However, in the wild, the average lifespan of a saki is between 10 to 15 years, roughly half that of captive monkeys.
Appearance
Noticeably one of nature’s most interesting-looking creatures, the Gray’s bald-faced saki typically sports a white and black coat of coarse, shaggy-looking hair. As their name suggests, the face of a Gray’s bald-faced saki is bare of most hair and unpigmented. Their coronal hair, the hair covering their heads, is pushed forward and acts as a sort of hood, covering the upper section of their faces. To many, this gives off the appearance of having bangs, truly putting the “bowl” is adorable.
Along with the long, shaggy coat of hair that covers most of their body, Gray’s bald-faced sakis have different hair types on the tops of their hands and feet, as well as on their underbelly and tail. The hair on their tail and torso is long while that on their hands and feet is a white, light, and fluffy coat that protects the skin.
Throughout their geographic range, coat color may vary by region. For example, in one area of Brazil a Gray’s bald-faced saki may appear lighter, while in another area of Bolivia, one may appear much darker. Environmental conditions, such as habitat type or climate, are likely causes of these differences. With this in mind, researchers have come up with a term to universally describe their unique color combination, “grizzled gray”.
Although their hair is naturally thick, when approached by potential dangers, the hair of a saki will piloerect. Piloerection, the bristling of hairs due to involuntary muscle contraction, allows this species to appear larger than it is. In instances of piloerection, the ultimate goal is to ward off predators and keep them away.
Considering sexual dimorphism, the systematic difference in form between individuals of different sex in the same species, the most noticeable difference between male and female Gray’s bald-faced sakis is that some males have neck folds, while females do not. Neck folds allow males to emit specific facial expressions, which can be useful when communicating to troop members, or to predators.
Diet
Gray’s bald-faced sakis are frugivorous seed predators. A frugivore is an animal that thrives on eating mostly raw or succulent type fruit products, such as roots, shoots, nuts, or seeds. Based on their preference for mature forest types with higher densities, large forest tree species are perfect for sakis, such as those found in the Lecythidaceae family. As seed predators, these plants would be perfect food sources! That being said, although 80% of their diets include unripe seeds, a Gray’s bald-faced saki may also consume fruit pulp, young leaves, flowers, and insects such as ants, spiders, or other arthropods.
As a frugivore, the Gray’s bald-faced saki may help or hinder fruit-producing plants by destroying seeds through digestion or dispersal. To combat seed predation, some plant species have evolved physical and chemical defenses to deter predators. For example, in order for a plant to prevent an animal from eating its seeds, the plant seed may evolve by changing its shape, thickness, or taste. Luckily for sakis, not all nuts are too tough to crack!
Behavior and Lifestyle
Since sakis are arboreal primates, when not foraging for food, most of their days are spent among the trees. Typically moving on all fours, these monkeys run, climb, and leap, using their non prehensile tails for balance support. Sometimes referred to as “flying monkeys”, Gray’s bald-faced sakis can leap up to 29.5 feet (9 meters) from one spot to another!
In the evening, because sakis never stay in the same tree for more than a couple of nights in a row, they travel across their home ranges in search of new trees every day. As a diurnal species, when days are spent foraging and nights are spent sleeping, it is important for sakis to remain alert, to avoid predation.
On the ground, terrestrial predators include the jaguar (Panthera onca), the giant anaconda (Eunectes murinus), the ocelot (Leopardus pardalis), or the tayra (Eira barbara). In the air, Gray’s bald-faced sakis have to watch out for avian predators like the harpy eagle (Harpia harpyja).
During daytime, saki monkeys spend between 9 to 12 hours traveling throughout the forest canopy. Watch out George, these guys are masters of the jungle!
Troops of Gray’s bald-faced sakis consist of between 2 to 9 individuals. In these groups, there is a single male and female breeding pair. The rest of the troop is made of juveniles and infants.
Allogrooming, a type of social grooming practice in which individuals groom one another to rid each other of insects and other parasites, is a very common practice among primates, especially when establishing dominance and hierarchy. During allogrooming, various troop members may groom, clean, and maintain each other’s appearance, especially between mothers and their offspring. Allogrooming reduces stress and strengthens social bonds.
While traversing their home ranges, it is not uncommon for multiple saki troops to run into each other. Because of their seemingly timid nature, rather than exhibiting aggressive displays to chase others away, these primates would rather ignore other troops or avoid them entirely. Unless they pose a direct threat, these monkeys are relatively non-confrontational.
To establish territorial boundaries, adult males scent mark their homes. Sakis scent mark their territory utilizing scent glands on their chests and throats, as well by urinating.
When predators are near, sakis attempt to stay as hidden as possible. If an area is deemed safe enough by the dominant male, the troop will slowly move away from the threat, camouflaged under forest cover. If all goes well, this technique allows them to evacuate safely and unscathed. Inversely, if this technique does not work, sakis will produce loud vocalizations such as trills, whistles, grunts, squeaks, or roars. Occurring in a series, once the first call is made, other troop members will mimic their leader’s call. In a best-case scenario, the sound will scare the predator enough that it will abandon its pursuit.
Although they typically communicate through sound or movement, facial coloration is another form of communication for bald-faced sakis. For example, facial blushing, an involuntary reddening of the face due to embarrassment or stress, is more evident in a species like the Gray’s bald-faced saki. This communication type can be very effective, especially when an individual wants to remain unnoticed by predators, yet communicate to its troop.
Gestation periods (length of pregnancy) for sakis lasts an average of 146 days, after which a female will give birth to a single offspring.
Infants cling to their mother’s underside or thigh for the first month of their life. In the few months that follow, they transition onto their mother’s backs and experience life by her side. After four months, the infant is able to walk independently, although it is still nursed by the mother. Once the infant reaches five months of age, it becomes more independent, slowly weaning itself from the mother’s care. At six months, the offspring is fully grown, fully weaned, and is able to survive on its own.
Females become sexually mature at around two years of age, while males become sexually mature around 3 years of age.
When ready to attract female attention, males will start developing their voices and will produce unique mating calls. Once a male is successfully able to call upon a female, the two sakis will mate.
Because troops typically have only one male and female breeding pair, Gray’s bald-faced sakis are often a monogamous species. That being said, because more captive Gray’s bald-faced saki populations are studied than wild ones, these creatures may engage in polyamory (having multiple mates). If that is the case, in a polyamorous relationship, there would either be multiple females mated to one male, or multiple males mated to one female. More evidence is needed to determine the accuracy of these claims.
The Gray’s bald-faced saki plays a critical role in seed dispersal for its ecosystem. As mentioned earlier, Gray’s bald-faced sakis are frugivorous primates. Benefiting many plant species, frugivorous primates disperse seeds via their feces. When sakis release seeds throughout their geographical range, they provide plant species with greater germination opportunities, promoting replenishment across vast areas of land.
Considering the ways in which plants and sakis benefit from this behavior, they have developed a mutualistic relationship. Mutualism is a relationship type in which interacting species are mutually benefited, and no one species is harmed. In this situation, both interacting species are fortunate to be involved in a relationship that prioritizes their combined ecological success and generational growth.
The International Union for Conservation of Nature lists the Gray’s bald-faced saki as Data Deficient (IUCN, July 25, 2024), appearing on the IUCN Red List of Threatened Species. The species’ current population trend is decreasing.
Due to their elusive nature, Gray’s bald-faced sakis are very hard to study in the wild. There is no accurate information on the population status of this species, but it is suspected to be declining due to habitat loss and hunting pressures. Unfortunately, sakis are subject to hunting for their hair and pelts.
The Gray’s bald-faced saki is not listed under an Appendix in the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival. This decision is likely due to the fact that the species is Data Deficient. Research needed to give this species larger context includes population size counts, population trends, population distributions, life history, and ecology.
Gray’s bald-faced sakis are included in international legislation and are subject to international management and trade controls. As this species occurs in parts of Peru, Bolivia, and Brazil, there are conservation sites throughout their home range, but the data is unknown.
If you are looking to help Gray’s bald-faced sakis, land and water management conservation actions could significantly increase this species survival rate.
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Written by Brooklynne Mitchell-Arno, July 2024