Geographic Distribution and Habitat
Napo sakis (Pithecia napensis), also known as Napo monk sakis, were first described in 1938. They are native to the rainforests of Ecuador and Peru, occupying a range south of the Rio Napo, from the city of Coca in the west to Yasuni National Park to the east. They live up to an elevation of 5,000 feet (1,500 m) and tend to prefer flooded forests, palm swamps, and terra firma forest. While they can be found in disturbed habitat, they tend to occur in higher population densities in mature forests.
Saki monkeys, those of the genus Pithecia, are a poorly studied taxon. This is primarily due to three factors: 1) they do not survive well in captivity; 2) the behaviors of those sakis successfully maintained in captivity are often very different from those of their wild counterparts; and 3) they are very shy and live high in the canopy, making them difficult to observe in the wild. Many life history traits are simply unknown for species of this genus, and their taxonomy has been a source of confusion for nearly 100 years. Since the Napo saki’s description in 1938 by Swedish zoologist Einar Lönnberg, they have been considered a subspecies of the monk saki (P. monachus). The Napo saki was elevated to full species status in 2014 after a taxonomic revision of the genus.
Size, Weight, and Lifespan
Adult sakis typically weigh between 2 and 4 lbs (1–2 kg), with a head and body length between 8 and 20 inches (20–50 cm). Their tails are approximately as long as their body. Their average lifespan is unknown, although a closely related species, the white-faced saki, is known to live to about 15 years of age in the wild and about 35 years in captivity.
Napo sakis exhibit slight sexual dimorphism. Males have a black body with a dense covering of short white hairs on the crown of their head, and a grey facial disk. They also sport a distinct rusty brown or orange ruff on their chest. Females are grey overall, with no facial disk or crown coloration. Their ruff is brown, and more subtle than the males’. Napo sakis have especially long hair around their face and neck. Their tails are also covered in long hair, giving them a very bushy appearance.
Napo sakis have various physiological adaptations to help them survive high in the rainforest canopy. They can exhibit piloerection (puffing out their body hair) to make themselves appear bigger than they are, which may help in territorial disputes or in fending off predators. Their hands have a split between their index and middle fingers which aids in gripping branches, and they have long, strong canine teeth used to bite into the tough coverings of the fruit they eat. Their forward-facing eyes allow them to see stereoscopically, a necessity for a life spent entirely in the trees.
Napo sakis feed primarily on fruits, supplemented with honey, leaves, and small animals such as mice, bats, and birds.
Behavior and Lifestyle
Napo sakis are shy and wary animals, and they live high in the canopy, preferring the tallest trees available, which often top 115 feet (35 m) in height. As a strictly arboreal species, Napo sakis occasionally descend to lower levels of the trees, but they almost never descend to the ground. They move about quadrupedally (on all fours), occasionally walking upright (bipedally) on thick branches, and can leap across gaps.
Napo sakis are named after the Napo River, an extraordinarily important water source that connects the Andes mountain range to the Amazon River. It supports the Ecuadorian rainforest, which is per square mile the most biodiverse region on Earth.
Napo sakis are diurnal (active during daylight hours), and live in pairs or small family groups with an average size of about 4.5 individuals. Although family groups live in defended territories, they have been observed sharing trees with other groups to sleep in at night. Males defend a home range of about 124 acres (50 ha) on average, while females patrol a smaller range of about 83 acres (33.5 ha) on average.
Saki monkeys communicate with chirps, whistles, and low calls for low intensity aggression, and use barks, grunts, and roars for more aggressive interactions. They recognize their mate with specialized vocalizations. Allogrooming—mutual social grooming—is used extensively by sakis to bond with groupmates.
Napo sakis are monogamous and pairs mate for life. They have one offspring at a time after a 170-day gestation period, and their generation length is ten years. When first born, infants clings to their mother’s bellies. As they start to wean, they move to clinging to her back. It is unknown what, if any, care is provided by the father or other members of the group.
Most of the time, Napo sakis are the only primate occupying their ecological role at the extreme top of the tallest trees in the forest. This means that interspecific competition with other primates is not an important factor for them. They may serve as important seed dispersers due to their largely frugivorous diet. There are no documented observations of Napo sakis being preyed upon, although there are several raptor species known to hunt the high canopy in the Napo saki’s range, such as the harpy eagle and black and white hawk eagle, and they may prey upon adult and/or juvenile Napo sakis.
Napo sakis are is listed as Least Concern by the International Union for Conservation of Nature (IUCN, 2015), as their habitat is largely intact and they are not subject to much human pressure throughout their range. However, their population is on a downward trend. Like other sakis, Napo sakis are occasionally hunted for food. Their reproduction is slow enough that it may be difficult for their population to recover after being overhunted. They are also at risk of habitat loss and from collection for the pet trade.
Napo sakis occur in protected national parks in Ecuador. They are listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), which restricts their trade. One of the most important priorities for Napo saki conservation is more research, as there are many gaps in basic knowledge about this species, and sound management decisions cannot be made without this information.
- Marsh, L.K. 2014. A Taxonomic Revision of the Saki Monkeys, Pithecia. Neotropical Primates 21(1).
Written by K. Clare Quinlan, June 2020