BALD UAKARI

Cacajao calvus

Geographic Distribution and Habitat
The bald uakari, or bald-headed uakari, is native to the Western Amazon—residing in the countries of Peru and Brazil, and possibly Colombia. Their rainforest habitat is in the Amazon River Basin, which often floods. Specifically, the bald uakari lives in várzea forests, seasonal floodplain forests that are inundated by whitewater rivers in the Amazon biome. Flooding occurs most often in the rainy season. To avoid the high water, these comely New World monkeys live in the trees alongside small tributaries or lakes.

Bald Uakari geographic range. Map: IUCN 2020

Size, Weight, and Lifespan
The bald uakari typically grows to 14-22.5 in (35-57 cm), and weighs anywhere from 4 to 7 lb (1.8-3.2 kg). Males are heavier than females. An average bald uakari lives anywhere from 15 to 20 years—though in captivity they can live longer, sometimes up to 30 years old.

Appearance
The bald uakari is most easily recognized by its red face and bald head, from which it derives its name. Some people compare them to old men and babies, because of their baldness; there is no denying this species is uniquely handsome. The striking crimson color is caused by blood-flow beneath the skin, specifically a thinner epidermis coupled with a higher concentration of capillaries in the face. The redness of a female’s face is correlated with her estrogen levels; the redness of a male’s face is indirectly related to his testosterone levels, according to a recent study. A redder face indicates a healthier monkey, since their faces, like ours, grow pale when they’re ill—particularly with malaria, which is rampant in their habitat.

Another distinction that sets the bald uakari apart is its conspicuously short tail, which is only around 6 in (52 cm) long. The bald uakari does not use its tail to travel through the trees; it relies on its arms and legs, as well as its long, furry fingers and toes. Their fur coats are long and cover the whole of their bodies, ranging in color from blonde to orange to brown to red. There are four recognized subspecies of bald uakari, distinguished by their variations in their coats. The subspecies with the palest coat is Cacajao Calvus calvus, or the white bald-headed uakari; the red bald-headed uakari has a red coat, and is classified as Cacajao Calvus rubicundus; the subspecies with a reddish gold coat and a black tail is Cacajao Calvus ucayalii; and, finally, Cacajao Calvus novasei is the most orange of the subspecies.

What Does It Mean?

Herbivore:
An animal that feeds on plants.

Polymorphic:

​Refers to when a trait occurs in two or more different forms, or “morphs” within a species. This accounts for different colorations of animals of the same species, or, in the case of the bald uakari, different forms of color vision.

Visit the Glossary for more definitions

Our thanks to Kyle Cody at Creecha Kids for this beautiful rendering of a bald uakari. Creecha Kids combines Art + Science for the best animal facts. ​Follow his work on Instagram @CreechaKids.

Diet
The bald uakari is an herbivore. The mainstay of its diet is fruit, which they find by foraging. Their foraging habits sometimes lead them to eat leaves, seeds, or roots—whatever is readily available, even insects, such as caterpillars. The diet of the bald uakari varies with the seasons and is dependent on flooding. When water levels are high and the uakari keep to the trees, they rely on fruit for nourishment. During the dry season, they leave the trees to search for food on the ground, particularly seeds. Their strong jaws allow them to eat tough foods that other animals would be unable to open—like unripe fruit or Brazil nuts.

Behavior and Lifestyle
Bald uakari are diurnal primates, which means they are active during the day. They are also arboreal primates, meaning they live in the treetops of the Amazon rainforest. They only come down from the trees during the dry season, when flooding ceases and there is food be found on the forest floor. They are foragers, not hunters, and are known to be territorial. A troop of uakari has a home territory of around 2 sq mi (500 ha). They are predominantly quadrupeds, but are also capable of walking and jumping on two legs, covering distances of up to 3 mi (5 km) in a day.

Fun Facts

A 2016 study revealed that the bald uakari has highly polymorphic color vision. This, researchers believe, aids them in foraging, when they have to be able to determine the colors of food against a leafy background, and also in sexual selection—since the redder the face, the more suitable the mate.

Daily Life and Group Dynamics 
Life can be very interesting within a troop of uakari. Troops are quite large—sometimes up to 100 monkeys, but more often around 30. The larger troop breaks down into smaller groups to go foraging for food, each sub-group being up to ten monkeys. Sometimes they even go off on their own to search for food. Since their troops are often so large, they are very social and playful primates—especially the young. Female monkeys typically stay where they were born; alternatively, male monkeys do not stay with their natal groups.

Communication
These monkeys mainly communicate acoustically, though on the whole they are pretty quiet. They will use shrieks as a method to defend their territory. Their hairless faces also allow them to be expressive and communicate emotions through their facial expressions.

Additionally, these monkeys wag their short tails to communicate. Their hair can also stand, which can be used to indicate territorial defensiveness. For mating, females release scents to attract males.

Reproduction and Family
Bald uakaris are most commonly monogamous. Females reach sexual maturity at the age of 3, earlier than males, who reach sexual maturity after 6 years. The average gestation period for a bald uakari is 182 days. The babies are nursed for as long as five months, and are provided for and protected by their mothers.

Ecological Role
The bald uakari is an herbivore, but relies so heavily on fruit for food that some might classify the species more specifically as a frugivore. Because they so often eat both ripe fruit and the seeds of fruit, the bald uakari plays an important role in seed dispersal, as do most frugivores. Monkeys are exceptionally important because they can transport seeds a greater distance than smaller animals.

Conservation Status and Threats
The bald uakari is listed as Vulnerable species by the International Union for Conservation of Nature (IUCN, 2020), appearing on its Red List of Threatened Species. Threatened by forest loss and hunting, the greater threat depends upon its range. Some regions are more heavily impacted by hunting. Others from deforestation.

Balk uakaris face challenges on multiple fronts. First, their reproductive habits lead to slow population growth. A female uakari only bears one infant every two years—and only one at a time. Indigenous peoples in the Amazon also hunt bald uakari. In Peru, they are used for food; in Brazil, they are often used as bait to hunt other species. Because they live along rivers, bald uakari are easy targets from boats. Human developments along waterways, including agriculture which transforms flooded regions, further exposes them.

The IUCN notes that bald uakari is possibly extinct from part of its native range in Colombia. In 1997, the Amazon Basin was the most heavily deforested region in the entire world. If the rainforests continue to be depleted by logging and other practices, we could lose this species entirely.

Conservation Efforts
This species is listed on CITES Appendix I. In March 2020, the IUCN reported the following conservation efforts:
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 programmes throughout Brazil. An international committee (Comitê Internacional para Conservação e Manejo dos Primatas Amazônicos) was established by the the CPB and Instituto Chico Mendes (ICM) to discuss and define actions for the conservation of Amazonian primate taxa, and together with the members of the Pitheciine Action Group (PAG), is currently developing Conservation Action Plans for each of the four subspecies in Brazil.

A decree (No. 34-2004-AG) was published by the Peruvian government in 2004 that approves the categorization of threatened Peruvian wildlife and prohibits hunting, capturing, owning, transporting, and exportation for commercial purposes. It is hoped that this will help in conservation actions and stimulate research on threatened Peruvian wildlife (Heymann 2004).

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 Worldwide Wildlife Federation is a prominent voice fighting for the Amazon. Organizations like the Amazon-Andes Conservation Program and IBAMA , the national environmental agency of Brazil, are cracking down on deforestation in the rainforests these monkeys call home.

References:

  • https://www.nationalgeographic.com/animals/mammals/b/bald-uakari/
  • http://rsos.royalsocietypublishing.org/content/2/7/150145
  • http://rspb.royalsocietypublishing.org/content/283/1828/20160067#sec-7
  • https://www.konicaminolta.com/kids/endangered_animals/library/field/bald-uakari/
  • http://www.arkive.org/bald-headed-uakari/cacajao-calvus/
  • http://www.theanimalfiles.com/mammals/primates/bald_uakari/
  • http://www.bbc.co.uk/nature/life/Bald_Uakari
  • http://www.iucnredlist.org/details/3416/0
  • https://animaldiversity.org/site/accounts/information/Cacajao_calvus/#behavior
  • https://www.youtube.com/watch?v=r_mB-23z4To
  • https://en.wikipedia.org/wiki/Bald_uakari#Conservation
  • https://en.wikipedia.org/wiki/Frugivore#Ecological_significance
  • http://eol.org/pages/326561/details

Written by James Freitas, March 2018. Conservation Status updated July 2020.