Geographic Distribution and Habitat
The bald uakari (pronounced ‘wakari’) is a small, red-faced primate native to the Amazon rainforest in South America.
Also called bald-headed uakaris, red uakaris, and scarlet fever uakaris, these primates have a limited distribution range across the Amazon River Basin in eastern Peru and western Brazil. They once inhabited southern Colombia but are assumed to have disappeared in that area because of deforestation.
Bald uakaris live in the tropical forests of seasonal lowlands called várzea (floodplain) forests. The largest populations (up to 30 monkeys) live along lakes and tributaries between the Yavarí (or Javarí) and Ucayali rivers, right along the border of Peru and Brazil.
Size, Weight, and Lifespan
The bald uakari is a medium-sized primate that weighs about as much as a small housecat—between 6.5 and 7.75 pounds (3–3.5 kgs). They grow to be between 15 and 22.5 inches (38–57 cm) long, with males averaging 17.9 inches (45.6 cm) and females 17 inches (44 cm).
They have the shortest tail of all South American monkeys, averaging 5 inches (15 cm). To put that into perspective, a similarly sized spider monkey’s tail can grow between 24 and 32 inches (63–82 cm) long.
In the wild, a bald uakari has a lifespan between 15 and 20 years. In captivity, they can live long enough to celebrate their 30th birthday.
The bald uakari isn’t your average South American primate. A bright red, hairless face is their most distinguishable characteristic, followed by large fangs, a short tail, and a body the size of a small housecat.
The bald uakari’s red face is caused by blood-flow beneath the skin—specifically a thinner epidermis with a higher concentration of capillaries in the face. The degree of redness is an indicator of health and the redder, the better. Just like humans, pale faces are a sign of illness and for the bald uakari that likely means malaria, which is rampant in their habitat.
Facial redness also plays a role in sexual selection. The redness of a female’s face correlates with her estrogen levels and a male’s correlates with his testosterone levels. That’s why males with intensely red faces are highly preferred by females.
The bald uakari’s conspicuously short tail is unlike other local primates. Measuring around 5 inches (15 cm), the non-prehensile tail is impractical for forest life. Instead, bald uakaris rely on their long arms, legs, fingers, and toes to travel through the trees.
Bald uakaris are covered in long fur all over, except their distinguishable bald face. Coat colors range in shades of blonde, orange, brown, or red. There are four recognized subspecies of bald uakari that are distinguished by their coat colors. The subspecies with the blonde, pale coat is Cacajao calvus calvus, or the white bald-headed uakari; the red bald-headed uakari, Cacajao calvus rubicundus, has a red coat; the subspecies with a reddish-gold coat and a black tail is called the red uakai, Cacajao calvus ucayalii; and, finally, Novaes’ bald-headed uakari, Cacajao calvus novasei, is the most orange of the subspecies.
Bald uakaris are both herbivores (plant-eaters) and frugivores (fruit-eaters), and their exact diet varies depending on the time of year.
During the dry season (August through November), their diet consists of fallen leaves and fruits, seeds, and roots. When flooding occurs during the rainy season (December through May), water levels become too high on the ground, forcing the bald uakaris to move up to the tree canopy, where they can find nourishment from fruits and leaves. Their strong jaws and developed fangs help them to bite through foods with hard exteriors, like thick fruit skins, unripened fruits, and Brazil nuts.
Behavior and Lifestyle
The bald uakari’s lifestyle is highly dependent on the season in the Amazon River Basin. When there is flooding during the wet season, bald uakaris are arboreal and live in the treetops of the Amazon, where they enjoy a fruit-heavy diet. During the dry season, they become terrestrial and roam the forest floor to forage for seeds and seedlings. Regardless of the season, bald uakaris are diurnal, meaning they are active during the humid days in the Amazon.
A troop (group) of bald uakaris typically maintain a home territory of 2 square miles (517 ha). Researchers say that the best time to observe bald uakaris is during the rainy season when fruits are more abundant and the monkeys travel in bigger troops.
Bald uakaris are quadrupedal, meaning they use all four limbs when walking and running on the ground and when traveling through the trees. On the forest floor, they also have the ability to walk and jump bipedally (using two legs). In a single day, the small primates can cover distances of up to 3 mi (5 km).
Their short, non-prehensile tails are purely decorative, so the bald uakari relies on their long arms and legs to move throughout the forest treetops. However, a bald uakari may wag its short tail when feeling excited or threatened.
Like many other South American primates, bald uakari have polymorphic color vision. This means that they have both dichromatic vision (they see in 2 different colors) and trichromatic vision (they see in 3 different colors).
Researchers believe this helps when foraging for colorful food against a leafy background. It also aids in sexual selection—the redder a male bald uakari’s face, the more desirable they are to females.
It’s a good thing bald uakaris are highly social because these monkeys live in large troops of up to 30 monkeys. Even larger troops of up to 100 have been observed.
Just like their diet, troop patterns and daily life depends on the season. When the forest is flooded, bald uakaris spend their days with their full troop up in the tree canopy. In the dry season when they are able to move on the ground, bald uakaris spend time foraging for food in smaller groups of up to 10 monkeys.
Babies cling to their mothers 24/7 until they are about 5 months old. Female bald uakaris start reproducing around age 3 and give birth to one baby at a time about every two years. Young bald uakaris are especially playful and can be a handful for a new mom, but luckily there are plenty of other monkeys in the troop to help out. Females stay in the same troop where they were born to care for their young. Males reach sexual maturity at age 6 and they do not stay with the same troop.
Bald uakaris live a quiet, but social, life gliding through the treetops and scouring for seedlings on the forest floor. They use vocalizations, facial expressions, pheromones, and body language to communicate. Their unique, hairless face is an advantage for communication. At least ten different facial expressions have been observed by researchers. To mark their home and defend their territory, bald uakaris produce shrieking sounds to ward off the unwelcome. During mating season, females release pheromones to attract males. Pheromones are chemicals that an animal produces that change the behavior of another animal of the same species.
Bald uakaris also wag their short tails to express excitement. But if the wagging is accompanied by clicking noises and erect fur, the bald uakari is feeling threatened.
Bald uakaris are primarily monogamous and a female gives birth to one infant every two years, on average. Females reach sexual maturity at the age of 3 while males reach maturity at 6. The breeding period is between October and May and after a 6-month gestation period, the female gives birth to a single newborn bald uakari.
Like other primates, newborn bald uakaris are small and helpless, making them vulnerable in their new environment. They are dependent on their mothers during the first few months of life, feeding only on maternal milk and clinging to mom constantly for protection. Around 5 months old, a bald uakari starts to wean off the mother by adding easy fruits to their diet.
Because they eat a diet of both ripe fruit and the seeds of fruit, bald uakaris are considered herbivores and frugivores. And like most frugivores, bald uakaris play an important role in seed dispersal, which is the process of transporting seeds to new areas.
Monkeys like the bald uakari are incredibly important for ecosystems because they can transport seeds greater distances than smaller seed-eating animals.
The bald uakari is listed as a Vulnerable species by the International Union for Conservation of Nature (IUCN, 2020), appearing on its Red List of Threatened Species.
Bald uakaris are threatened by many things. Deforestation continues to destroy bald uakari habitats and deplete food supplies, resulting in a declining population. In the last 50 years, the Amazon in Brazil has lost over 275,000 square miles of forests, which is ⅕ of its total forest cover. In 1997, the Amazon Basin was the most heavily deforested region in the world, leading to the assumed disappearance of the Colombian bald uakari population.
They are also susceptible to indiscriminate hunting by indigenous peoples. In Peru, they are used for food; in Brazil, they are used as bait to hunt other species. Because bald uakari live along rivers, they are easy targets from boats. Human developments along waterways, including agriculture which transforms flooded regions, further exposes them.
Since females are only able to give birth to a single infant every two years, the species cannot keep up with the declining population numbers. If deforestation continues to deplete the rainforest through logging and other practices, we could lose this species and many others forever.
Deforestation is a primary concern for the future of the bald uakari and the Amazon, but efforts are being made to better protect the rainforest. Organizations such as the Worldwide Wildlife Federation; IBAMA, the national environmental agency of Brazil; and the Amazon-Andes Conservation Program support anti-deforestation and conservation efforts all throughout the Amazon. Fortunately for the bald uakari, efforts to save the rainforest will also benefit the species, along with the other animals who live in the same area.
The IUCN reports that the Primate Protection Centre (Centro de Proteção de Primatas Brasileiros: ICM/CPB ) of the Federal Environmental Protection Institute (Instituto Chico Mendes) supports and coordinates primate conservation programs throughout Brazil. An international committee was created to discuss and define actions for the conservation of Amazon primates, and is in the process of developing conservation act plans. The Peruvian government also published a decree in 2004 that prohibits hunting, capturing, owning, transporting, and exporting wildlife for commercial purposes.
Written by Maria DiCesare, May 2022