At first glance, male and female white-faced sakis can look like different species. Adult males have jet-black fur and a white face, while females are covered in brownish-grey fur and lack the iconic mask. Instead, females have pale tan or whitish stripes around the nose and mouth. Both sexes are similar in size, weighing 1.5 to 2.5 kilograms (3.3 to 5.5 pounds) and measuring about 30 to 35 centimeters (12 to 14 inches) in body length.

They also share a long, bushy tail roughly equal in length to their body. It isn’t prehensile, meaning it can’t grasp branches, but it helps them balance as they leap through the trees. Their shaggy coats make them appear larger than they are. When curled up, they can resemble clumps of moss from a distance, providing useful camouflage. Their thick fur also repels rain in the jungle.

White-faced sakis live in the rainforests of northern South America, mostly within the Amazon Basin. They’re found in Brazil, Venezuela, Guyana, Suriname, and French Guiana, primarily north of the Amazon River. They stick to dense forest habitats and never venture into grasslands or mountains.

They inhabit both lowland and upland rainforests, including seasonal swamps and river-edge forests, as long as the areas aren’t permanently flooded. Sakis prefer forests with plenty of fruiting trees and reliable water sources. They’re often seen 15 to 25 meters (50 to 80 feet) up in the canopy but will sometimes descend to lower branches or even to the ground to forage. At night, they sleep high in the trees, tucked into leafy spots for cover. They rarely use the same sleeping site twice, likely as a way to avoid predators.