WHITE-FACED SAKI

Pithecia pithecia

Geographic Distribution and Habitat
The white-faced saki is a New World monkey found in rainforests throughout the northeast region of South America in northern Brazil, French Guiana, Suriname, Guyana, and Venezuela. They are usually found in the lower-to-mid canopy of the forest. These monkeys are generalists who can adapt to both wet and dry conditions in a variety of altitudes with relative ease.

White-faced saki geographic range, IUCN 2018

Size, Weight, and Lifespan
Although data is sparse, males seem to be slightly larger than females, on average. Studies show the male white-faced saki weighs between 4 and 5.2 lb (1.8–2.4 kg), while the female’s weight ranges 3 to 4.1 lb (1.35–1.89 kg). Both sexes have similar body length of 12.5 to 16 in (32–40 cm), with tails usually matching their body length.

In the wild, white-faced sakis have a life expectancy of 15 years, although captive sakis have lived into their mid-thirties.

Appearance
Despite their name, only male white-faced sakis have the signature white face. Males have thick white and yellow fur covering their face, making them easily recognizable. Their face provides a sharp contrast to the rest of the body, which is covered in long black fur. Females, on the other hand, are more drab colored, with short fur covering their bodies in gray, brown, and red. Females also have less hairs surrounding their eyes and snout.

White-faced sakis can also be noted for their bushy tail, which is non-prehensile, meaning that it cannot grab onto branches. Their throats are almost naked, which makes it easier to scent mark trees using the oils secreted from the gular gland. These unique-looking monkeys also have characteristically flat noses.

Their long, skinny fingers and toes have thick pads on the tips to give them a better grip on branches. The wide separation between the thumb and index finger allows them to climb up thick branches and trunks with ease.

What Does It Mean?

Activity Budget: 
A way to quantify animal behavior by observing an animal over an extended period and documenting activity. An activity budget demonstrates how much time an animal spends in various activities such as eating, resting, sleeping, and moving.

Arboreal:
Physically adapted to living primarily or exclusively in trees, such as arboreal-dwelling (tree-dwelling) monkeys.

Diurnal:
Active during daylight hours.

Ecosystem:
A biological community of interacting organisms and their physical environment.

Monogamy:
A mating system in which a male and female mate exclusively with each other.

Nonprehensile or Non-prehensile:
Incapable of grasping or gripping (opposite of prehensile: capable of grasping).

Subadult: 
An animal who is not fully adult.

Visit the Glossary for more definitions

Diet
White-faced sakis rely on fruits and seeds for roughly 90% of their diet. They have thick and strong teeth designed to crush seed shells and peel away at fruit. Sakis have also been known to eat young leaves (as opposed to mature leaves which are more toxic), flowers, insects, and occasionally other small animals.

Behavior and Lifestyle
An activity budget of white-faced sakis found that individuals spend about 26% of their day foraging, 30% traveling, and 44% resting. As diurnal animals, they are most active during the day. The saki is a primarily arboreal monkey, spending almost their entire life in the trees.W

White-faced sakis awake in the early morning and travel from tree to tree, making leaps of up to 33 ft (10 m) in length. They may travel over a mile in a single day in search of foraging patches.

Daily Life and Group Dynamics 
The make-up of one group of white-faced sakis can vary greatly from another group. Although the average group of sakis contains about 4 individuals, researchers have observed groups numbering anywhere between 2 and 12 sakis.

Groups of sakis hold established territory and will defend it from invaders, although conflicts rarely turn violent. Instead, conflicts often feature loud grunts and squeals, branch shaking, and chasing. As with most animals, violent interactions do more harm than good for the species as a whole, and it is evolutionarily advantageous to avoid them.

Fun Facts

White-faced sakis are nicknamed “flying monkeys” for their exceptional ability to leap from tree to tree.

Communication
Mating pairs of white-faced sakis establish their territories and reinforce their bonds by performing vocal duets that ring through the forest. Their vocalizations range from whistles to growls, chucks, and trills.

Adult males are also avid scent markers, marking their territory using combinations of urine and their gular gland near their throat. 92% of all scent markings are made by adult males. Males tend to mark trees rich in fruit, which other sakis are more likely to visit.

Reproduction and Family
Researchers originally thought white-faced sakis were monogamous, but more intense research in the wild revealed that many of the monkeys were not monogamous. The original misconception was due to the fact that most research was conducted in captive environments with small populations. Captive female sakis also tend to give birth earlier in life than their wild counterparts, often resulting in long-term health problems, which may shorten their lifespan. The unusually high difference in behavior between captive and wild sakis can lead to contradictory findings from separate researchers.

White-faced sakis reach sexual maturity between 32 and 37 months old, although some females may take a few months longer to mature. A mother’s pregnancy will last about 146 days (almost 5 months) and she will almost always give birth to a single offspring. Twin white-face sakis have never been observed, although the data are sparse.

Mothers carry their babies for 3–5 months and continue to nurture their offspring until they have matured. The baby’s sub-adult siblings will also help raise the baby if they still live with their parents, learning how to raise babies of their own in the future.

Ecological Role
With fruits and seeds being a major part of their diet, white-faced sakis are major contributors to seed dispersal. As the seed passes through the monkey’s digestive system, the saki may travel over a mile away from the parent tree. This means that the offspring plant can grow without having to compete with its parent for resources. This also ensures a more diverse forest, which creates an ecosystem more resistant to both biotic and abiotic threats.

The most common predators for sakis are large birds of prey, such as the harpy eagle (the world’s largest eagle). Other predators include snakes, jaguars, and tayras (a member of the weasel family). Sakis avoid predation either by hiding (from larger and stronger animals like eagles or jaguars) or by ganging up on the attacker.

Conservation Status and Threats
The International Union for Conservation of Nature gives the white-faced saki a Least Concern status (IUCN, 2015). They report that the population is widely distributed, is not fragmented, is found in numerous protected areas, and faces no major threats. However, the white-faced saki is a difficult species to study in the wild and there is no precise population estimate. The main threat is hunting and habitat loss. They are sometimes found in the pet trade.

White-faced sakis are common in the pet trade. The species is listed in Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning that trade must be controlled so that they do not become threatened in the future.

Conservation Efforts
Although white-faced sakis are not seen as a major to concern for conservation groups, the species benefits from living alongside vulnerable animals such as the jaguar and the West Indian manatee. At least 16% of white-faced sakis live in legally protected habitats in Suriname and Guyana.

The white-faced saki is difficult to study in the wild, but since this monkey’s wild behavior seems so divergent from their captive behavior, it is important to further study the animal in the wild.

References:

  • https://alltheworldsprimates.org/Members/Home/MasterPrimate.aspx?tid=247
  • https://animaldiversity.org/accounts/Pithecia_pithecia/
  • http://www.iucnredlist.org/details/43942/0
  • https://www.lpzoo.org/animal/white-faced-saki-monkey
  • https://nationalzoo.si.edu/animals/pale-headed-saki-monkey
  • Gregory, Tremaine. “Comparative Socioecology of Sympatric, Free-ranging White-Faced And Bearded Sakis in Brownsberg Nature Park, Suriname.” Kent State University, 2006.
  • Norconk, Marilyn. (2006). Long-term Study of Group Dynamics and Female Reproduction in Venezuelan Pithecia pithecia. International Journal of Primatology. 27. 653-674.
  • Thompson, Cynthia L. “Non-Monogamous Copulations and Potential Within-Group Mating Competition in White-Faced Saki Monkeys (Pithecia Pithecia).” American Journal of Primatology, vol. 75, no. 8, 2013, pp. 817–824.

Written by Eric Starr, June 2018