Miller’s saki, Pithecia milleri
MILLER'S SAKI
Pithecia milleri
Geographic Distribution and Habitat
Miller’s sakis are endemic to southwestern Columbia and northeastern Ecuador. They are found in the lush forests surrounding Florencia, capital of the Caquetà department in southern Colombia. This region is known as the Golden Gate of the Amazon for its rich fauna and flora biodiversity. Populations of Miller’s sakis also spread east to protected wet and flooded forests of La Macarena and La Paya National Parks in the departments of Meta and Putumayo respectively. These primates live in a tropical, humid, and warm climates all year with temperatures ranging from 66°F (19°C) to 86°F (30°C).
In Ecuador, Miller’s sakis inhabit the moist forests north of the Rio Napo, another biodiversity hotspot famous for its large number of palms, orchids, llanas, epiphytes, towering canopy trees, and dense understory vegetation.
These primates have a large distribution range because they have the ability to thrive in various forest types—from “várzea” or seasonal floodplain forest inundated by whitewater rivers, to “igapó” or blackwater-flooded forests, to “terra firms” or solid earth forests. They are adaptable and can survive in fragmented forests but larger populations are found in continuous mature forests.
Current data indicates that these animals are found at altitudes ranging from 1640 to 2950 feet (500 to 900 meters) above sea level on average; and at altitudes of 650 to 3500 feet (200 to 1,070 meters) on the eastern mountain range in Colombia.
Even though there is no official record confirming it, Miller’s sakis are thought to be present as well across the Peruvian border in the Zona Reservada Güeppi.
There has been a lot of confusion regarding saki monkeys in the Pithecia genus over the years. First, taxonomists (from the 18th to the 20th century) used the term “beard” to refer to the chest ruff of these animals, when they do not have a beard. Second, many specimens in museums were labeled incorrectly because there hadn’t been enough field observation and the anatomy of females and sub-adult males was not understood.
Miller’s sakis were first identified as a species by American zoologist Joel Asaph Allen in 1914. However, in 1987, mammalogist Philip Hershokovitz and primatologist Thomas Defler disagreed with the initial assessment and demoted the species to a subspecies of the Monk saki. In 2014 new studies by Laura Marsh identified 16 species in the genus Pithecia and reinstated the Miller’s saki as a species in its own right.
Size, Weight, and Lifespan
Miller’s sakis are rather small. They measure 12 to 16 inches (30-40 cm) from head to toe and weigh approximately 4.5-5.5 pounds (2-2.5 kg). Females are smaller than males, but not enough for one to easily distinguish a male from a female by size alone.
Their beautiful furry tail is roughly the same size as their body—i.e. 15 inches (38 cm) long.
The lifespan of the Miller’s saki is likely similar to that of the closely related monk saki which can live between 14 and 18 years in the wild.
Appearance
Miller’s sakis have a thick layered woolly pelage that is peppered with grey. Interestingly, the chin and the underside of the neck are bare. Males and females are dichromatic which means they have different coloring. Males are darker than females and have some brown fur on top of the head, forearms, and ankles. The fur on the trunk is longer than the hair on the forearms and hind limbs. Females are grey all over, including the face, and they are slightly smaller than males. Male juveniles look like their mother until they reach maturity.
These monkeys have two distinctive white stripes (called malar stripes) that look like parenthesis circling the eyes and framing the mouth. The thin white mustache that delineates their upper lip makes them look a bit sad. The fur covering their heads is unique and is reminiscent of a haircut in the style of the ’60s rock band, the Beatles. Their ears are hardly visible.
Their whitish hands and feet have five digits with an opposable thumb and big toe—a great adaptation that allows them to grasp and hold onto food items and branches. Their hindlimbs are much longer than their forelimbs which explains why they are such great leapers. They have a long bushy tail.
When they are threatened, they can fluff up the hair on their body and tail to make themselves appear bigger than they are. This is called piloerection—a reflexive response to cold, shock, or fright that causes the muscles at the base of hair follicles to contract—similar to goose bumps in humans.
Diet
The diet of Miller’s sakis’ consists of fruit, seeds, young leaves, flowers, insects, and arthropods—specifically army ants and spiders of which they are very fond. Miller’s sakis are considered “seed predators” because seeds are one of their main staples, the second most important is fruit. Together, seeds and fruit provide these animals with the glucose, carbohydrates, fat, and protein they need to be healthy and have energy. Miller’s sakis also supplement their diet with flowers, bark, and leaves—but these are high in cellulose and harder to digest.
Such dietary flexibility allows these cute creatures to survive in various habitats and not compete directly with other primate species that live in the same forest patches. The saki monkeys’ teeth are adapted to such a varied diet. The upper and lower incisors are forward-tilted and function as pincers which are perfect for plucking leaves. The splayed canines easily cut through the flesh of fruit and the strong flat molars crush and masticate seeds.
Behavior and Lifestyle
Miller’s sakis are arboreal—meaning they live in trees. Their principal mode of locomotion is leaping from branch to branch, but they also walk or run quadrupedally (on their hands and feet). Their long legs allow them to make long leaps to travel fast in the canopy and escape from predators. This great ability to leap earned them the nickname “flying monkeys”. Their long, bushy tail is not prehensile (meaning they cannot grasp objects) but is used for balance and steering when they leap long distances between trees. They have also been observed swinging their body from side to side before leaping.
Miller’s saki monkeys can take long leaps between branches and are sometimes referred to as “flying monkeys”.
These unusual-looking primates were named after Leo Miller who, in 1912, collected an adult male specimen currently at the American Museum of Natural History in New York.
Miller’s saki monkeys typically live in small family groups of up to 9 individuals. They are diurnal, which means they are active during the day. They travel 0.9 to 1.2 miles (1.5 to 2 km) daily to forage for food and the group territory extends usually between 3.8 and 9.6 square miles (10-25 km2). The distance traveled during the day to forage depends on the season and if food is readily available.
Very little fieldwork has been done on these primates but some observers reported seeing a few individuals bundled up on tree branches at night to sleep.
Although there is no documentation regarding grooming, it is likely Miller’s sakis do groom each other. Grooming reinforces social bonds between individuals and helps maintain a healthy coat and skin by getting rid of parasites.
Miller’s sakis share the forest and its resources with many other animals, including the Caquetá titi monkeys (Plecturocebus caquetensis).
Miller’s sakis communicate vocally with grunts, chirps, whistles, and low calls. Vocalizations have different meanings—they can indicate the location of an individual, coordinate movements of the group, identify predators, or claim and defend a territory. According to recent studies, vocalizations can be specifically directed at ambush predators—like ocelots—and successfully persuade them to abandon the hunt. Both males and females have glands on the throat that they rub against tree branches to scent mark them, thereby leaving odorous messages to other Miller’s sakis. A lot of information is passed on through scent—such as the gender, health, and reproductive status of each individual animal.
Not much is known yet about Miller’s sakis family life and reproduction, but looking at how monk sakis are organized, we can get a pretty good idea of how these animals live in a family setting. There is also a lot more data on the closely related white-faced saki. Refer to New England Primate Conservancy’s monk saki and white-faced saki Primate Species Profiles.
Groups are thought to be composed of an adult female, an adult male, and juveniles. The pair may or may not be monogamous—the jury is still out. There may also be some groups composed of several unrelated adults.
It is likely that Miller’s sakis breed seasonally and that births coincide with the time of year when food is most abundant. As for most primates, twins are rare and mothers typically give birth to one offspring. Male babies look like the mother until they reach adulthood and take on the color characteristics of adult males by the time they reach maturity.
Miller’s sakis eat fruit, so they contribute to the regeneration of the forest by spreading pits or seeds through their feces. They also eat seeds, which means those seeds are masticated and don’t spread through the animals’ feces. Their role is therefore not quite clear and more studies are needed.
The Miller’s saki is classified as Vulnerable on the International Union for Conservation of Nature Red List (IUCN 2021). Their population is projected to decline 30% by 2047; however, because these animals are shy and difficult to observe, data is insufficient to have an accurate count of individuals in the wild. Most of the observations of Miller’s saki monkeys have been done in the department of Caquetá. A few other reports were completed in Serranía de la Macarena National Park by the Humboldt Institute and the University of Kyoto. More field studies are needed.
Saki monkeys are threatened by deforestation due to land conversion for farming and timber harvesting. The Global Forest Watch statistics project a 10% to 30% loss of forest coverage within the next two decades both in Colombia and Ecuador.
In Ecuador, oil drilling highly contributes to deforestation since the early 1960s—especially as new roads get built to access the drilling sites.
There is no documentation of predation on Miller’s sakis, but harpy eagles may prey on them. As with most exotic wildlife on earth, saki monkeys are also affected by the illegal pet trade. They may also be victims of subsistence hunting—although some cultural beliefs act as a deterrent to eating the meat of saki monkeys. For instance, the Amazonian Quechua of Ecuador think the flesh of these animals is toxic and should not be fed to young children or dogs, lest they become ill or die.
The Miller’s saki is listed in Appendix B of the Convention on International Trade in Endangered Species (CITES) which restricts the trade of wild animals and plants.
Field research and the protection of the forests in which Miller’s sakis live are essential to their survival. In regard to the Miller’s saki habitat, many organizations are working with indigenous people to protect the ecosystem of the Amazon in Ecuador. And in Colombia, the Ministry of Environment signed the Cartagena del Chairá Agreement in Caquetá last year. This agreement acknowledges the importance of preserving the country’s forests and mitigating the impact of pollution, climate change, and the loss of biodiversity.
- Marsh, L. K. “A taxonomic revision of the Saki monkeys, Pithecia Desmarest, 1804.” Neotropical Primates, vol. 21, no. 1, pp. 1–163, Jul. 2014. doi: 10.1896/044.021.0101
- Diet and dental topography in pitheciine seed predators – Justin A. Ledogar, Julia M. Winchester, Elizabeth M. St. Clair, Doug M. Boyer
- Climate in Caquetà – Climate Data website (en.climate-data.org)
- The Napo Moist Forests: A Biodiversity Hotspot in the Amazon Basin – lacgeo.com
- New World Primates – Ecology, Evolution, and Behavior – Warren G Kinsey
- Adaptive Radiation of NeoTropical Primates – Marilyn A. Norconk, Alfred L. Rosenberger, Paul A. Garber
- An Introduction to Primate Anatomy – Friderun Angel-Simons
- news.mongabay.com – Scientists uncover five new species of “toupee” monkeys in the Amazon – Jeremy Hance
- Neotropical primates (23/2), December 2017 – article: “Aportes al conocimiento de la distribución del mico volador epithelia miller (Allen, 1914) en el occidente amazónico colombiano” – Javier García Villalba, Andrés Páez y Erwin Palacios
- Neotropical primates (25/1), December 2019 – article: Primer registrode epithelia miller (Allen, 19140 en la Baja Bota Caucana, corregimiento de miraflor, municipio de Piamonte, Cauca
- Oil roads to ecological ruin: Ecuador’s bushmeat and wildlife trade – Sean Mowbray
- scientificameerican.com “Monkeys Use Alarm Calls to Tell Predators to Scram” Jason G Goldman
- UNEP-WCMC technical report – AC28 Doc. 21.1 Annex 9 – “Animal Taxonomy and Nomenclature”
- www.gcftf.org/historic-agreement-in-caqueta – Colombia signs Historic Agreement against Deforestation in Caquetá (Jan 26, 2024)
Written by Sylvie Abrams, February 2025