Geographic Distribution and Habitat
The black-headed uakari was declared a distinct species in 2008 due to its genetic, morphological, and ecological differences from other uakari species. Also known as the golden-backed uakari, golden-backed black uakari, and Homboldt’s black-headed uakari, this New World monkey lives in northwestern Brazil, southeastern Colombia, and southwestern Venezuela. Occupying the Amazon River basin, the species’ range is confined in the south and west by Colombia’s Rio Negro, the largest tributary of the Amazon and the largest blackwater river in the world, Brazil’s Rio Marauiá in the east, and Venezuela’s Canal Cassiquiare and Rio Orinoco to the north.
Seasonally inundated blackwater-flooded forests, known as igapó forests, are this primate’s preferred habitat. However, black-headed uakaris also inhabit upland nonflooded forests, known as terra firme forests; montane forests, located on mountainous slopes within a specific climate range; and white-sand forests, which are rare subtropical forests distinctive for their unique combination of plant and animal species and their restriction to ancient coastal dunes, typically composed of clay soils and nutrient-deficient white sands.
Arboreal by nature, that is, they spend all their time in the trees, black-headed uakaris can be found at elevations of 328 to 5,000 ft (100 to 1,500 m) above sea level.
TAXONOMY IN TRANSITION
Who’s that monkey in the tree?
The black-headed-uakari has a rather confusing “family tree” (an apt pun for this arboreal species!). Let’s see if we can figure out who’s on each branch (last pun!)!
Initially, scientists believed that the black-headed uakari (Cacajao melanocephalus) had the following two subspecies:
- Golden-backed uakari (Cacajao melanocephalus ouakary)
- Black-backed uakari (Cacajao melanocephalus melanocephalus)
Then, in 2008 using morphological and molecular analyses, scientists discovered a new black uakari species. Their discovery led them to reclassify the name golden-backed uakari as a “junior synonym” to the “senior synonym” name of black-headed uakari. Say, what? This is just fancy science-talk to convey that a single species might be known by two different names. Usually, the earlier name (the senior synonym) is given preference in referring to a species. However, these pioneering scientists decided to buck zoological nomenclature rules and replace the senior synonym with the junior synonym’s name. So, this is why you’ll find the species referred to first as “golden-backed” and second as “black-backed”—in some scientific circles.
And what about that second subspecies, the black-backed uakari? Scientists elevated this species to Neblina uakari (Cacajao hosom), a species that is Vulnerable to extinction due to hunting. And the newly discovered black uakari? Scientists named this species: Aracá uakari, or Ayres black uakari (Cacajao ayresi).
All this family genealogy is nebulous, however; scientists are constantly reassessing the species.
Remember all this when you play primate trivia!
Bonus points! Instead of using “junior synonym” or “senior synonym” to refer to the naming of a species, try out the word “neotype.” A neotype refers to “a type of specimen that is selected subsequent to the description of a species to replace a preexisting type—most often, of one that has been lost or destroyed.” Of course, the black-headed uakari has neither been completely lost, nor destroyed–yet. With your newfound knowledge of the species, you can help raise awareness for greater conservation of the species so that the black-headed uakari does not vanish from our world.
Size, Weight, and Lifespan
Males have a more robust build than the females of this species, and are also equipped with bigger canine teeth.Head-to-body length for black-headed uakaris is 12 to 20 in (30 to 50 cm); males average 16 in (41.5 cm), and females average 15 in (39 cm). Tail length is about one-third of the primate’s head-to-body length, adding only another 5 to 8.25 in (12.5 to 21 cm). Black-headed uakaris’ tails are considered to be relatively short for an arboreal species and are nonprehensile (incapable of grasping), a characteristic that perplexes scientists. A small sampling of male black-headed uakaris puts the species’ weight at 5.3 to 9 lb (2.4 to 4 kg).
Uakaris can live up to 20 years old in the wild.
With wild black hair sticking out from every direction, it’s easy to imagine that this monkey is having a bad hair day. Big brown eyes peer out from an expressive face with black hairless skin. The snout is somewhat flattened, and random whiskers shoot out from the monkey’s upper lip and chin. Head, shoulders, arms, and lower legs are covered by lustrous black hair; chestnut-brown highlights adorn the uakari’s furry chest. A long fur coat that looks a bit like an orange bathrobe covers the back, upper thighs, and extends to the uakari’s poofy tail. The uakari’s hands and feet are black and hairless.
What Does It Mean?
A type of social hierarchy that arises when members of a social group interact, often aggressively, to create a ranking system. In social living groups, member are likely to compete for access to limited resources and mating opportunities.
Refers to a living organism’s distinct physical (biological) characteristics.
Visit the Glossary for more definitions
Black-headed uakaris are primarily frugivorous, which means that they eat a lot of fruit — especially hard-shelled fruits. Some scientists classify this species as a sclerocarpic frugivores, a specific term that refers to an animal whose diet consists primarily of hard-shelled fruits and seeds. In Colombia, their most important fruit species is Eschweilera.
Black headed uakaris also have a penchant for unripe seeds, particularly from the tree species Micrandra spruceana, Eperua leucantha, and Hevea braziliensis. The unique dietary adaptation that enables them to digest unripe seeds also allows black-headed uakaris to inhabit certain types of forests that are less hospitable to other primate species, due to more limited edible food sources. During the dry season, when fruit is scarce, the species migrates away from the igapó forests.
Pulp and leaves are also on the black-headed uakari’s menu. So are insects; in the dry season, when fruits are scarce, black-headed uakaris are known to eat a large quantity of caterpillars.
Behavior and Lifestyle
Black-headed uakaris engage in a variety of types of locomotion when traveling through the forest canopy. They can move quadrupedally (on all fours), oftentimes galloping or bounding, with their forelimbs moving forward together followed by their hindlimbs moving together as one unit. Or they might clamber forward with their body in an almost horizontal position (known as pronograde clambering). They leap across gaps between trees, first gaining enough momentum for this feat by rocking themselves back and forth on a branch and then pushing off. Adult males, being larger than the females, are less graceful when it comes to leaping.
Traversing between the tips of tree branches or twigs takes acrobatic skill, which black-headed uakaris demonstrate by bridging. Rather than try to balance on these weak tree supports, the uakaris evenly distribute their weight, fling their forearms forward to the new support facing them, and then bring forward their hind limbs one at a time to advance to the new support. (One might ask whether hanging out with common squirrel monkeys inspired this behavior!)
Brachiation (swinging by the forearms from branch to branch) is sometimes used, but most often between juvenile black-headed uakaris during play sessions. Likewise, with bipedal locomotion (upright walking): black-headed uakaris are capable of this feat—if a surface is flat—but juveniles are the ones who typically engage in this mode of locomotion when play-chasing one another.
And although the tails of black-headed uakaris offers them no assistance in balancing or grasping, they are able to suspend themselves by their hindlimbs.
Daily Life and Group Dynamics
Average group size of this exclusively tree-dwelling species—black-headed uakaris have never been observed on the ground—ranges from 10 to 30 individuals. However, in habitats with an overabundance of food, groups as large as 100 individuals have been observed. Mixed-gender groups of multiple males and females are the norm; dominance hierarchy has not been recorded for this species.
Black-headed uakaris are diurnal, meaning that they are active during daylight hours. They travel widely, sometimes outside their normal range, in large, flexible groups, up to 2.5 mi (4 km) each day. Scientists have observed that the Colombian population of this primate engages in a practice known as “fission-fusion.” Simply put, these uakaris split up into smaller numbers to forage(fission) and then come back together as one large group (fusion) at the end of a day of foraging. Scientific speculation is that primate fission-fusion societies may allow for a more efficient and economic foraging mode. Scientists did not observe this behavior in Brazil’s black-headed uakari population.
When foraging, black-headed uakaris will pick an immature fruit from a tree and carry it to a larger branch to consume. Their strong hands and feet and opposable thumbs assist them.
Juvenile black-headed uakaris often tag along with adult females, with the two generations pausing in their travels to engage in extended periods of social grooming.
Black-headed uakaris communicate with one another through a wide array of vocalizations, visual cues, tactile behavior, and olfactory signals.
Vocalizations often accompany daily activities such as foraging, feeding, traveling, solitary and group rest, and long-distance interactions. Common calls include the “tcho,” a loud call emitted by adults, with the mouth wide open; the twitter, a low-frequency call, short in duration; the chirp, used to maintain contact between group members; the sharp whistle, a high-pitched scream; the short whistle, a brief call emitted by juveniles, in response to an “ough” call; the “ough,” a brief call emitted by adults to get the attention of juveniles; the hiss, emitted by juveniles during play; the loud scream, a boisterous, enthusiastic call emitted singly or in a series that is relatively rare; the “hic,” a staccato, fragmented call emitted in a series in response to certain stimuli, performed by all individuals except adult males; the “ahh,” a quiet call that sounds like a faint exhalation of breath (think of a sigh) emitted by both juveniles and adults during playful and aggressive displays.
Visual cues include piloerection, a physical display that occurs when the primate’s hair stands on end (or piloerects). Used to convey fear and aggression, this performance gives the illusion of making an individual look larger. Both sexes exhibit this behavior, from older juveniles to senior adults. Tail wagging is used after squabbles and at the end of grooming and conveys general arousal on the part of the sender; it is performed by both sexes, from older infants to senior adults.
Social grooming is the most common tactile behavior. Besides reinforcing social bonds with one another, social grooming helps to remove dead skin and parasites.
Olfactory signals include sniffing; used to say “hello,” one black-headed uakari individual will bend down and sniff the genitalia of another—akin to the way that dogs say “hello” to one another!
Both sexes have a sternal gland (in the chest wall) which scientists think might be involved in olfactory communication. Finally, females emit a scent to attract a male suitor for breeding.
Reproduction and Family
The black-headed uakari is a polygynous species; that is, the male gets to mate with multiple females. Males reach sexual maturity at six years of age, and females are considered sexually mature at three years of age. After an unknown gestation period (not recorded in scientific research), females give birth to a single infant, every two years. Births occur between March and April at the onset of the rainy season when fruit is most plentiful.
Infants are small and vulnerable at birth. They cling to their mothers for their first few months of life, nursing. They are considered weaned at about four months of age, when they begin to forage with their group for soft fruits and seed pods. When they grow bigger and older, their large canines will assist in eating hard-shelled fruits, and their strong incisors will help them tear through husks to get to seeds.
Because they so often eat both ripe fruit and the seeds of fruit, the black-headed 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 black-headed uakari is categorized as Least Concern by the International Union for Conservation of Nature (IUCN, 2020), however their population trend is decreasing. Overall, the species has a large geographical range and occurs in a region which has been impacted comparatively little by habitat disturbance. Although locally hunted for meat and for fishing bait, black-headed uakaris are usually not the preferred game species where it occurs.
The black-headed uakari is listed in Appendix I of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival. Other than the species’ listing in CITES, no specific conservation measures exist for the black-headed uakari.
Although the black-headed uakari population that lives within the Neblina transboundary preservation areas is considered “protected,” this status is somewhat meaningless; poachers ignore the preserve’s wildlife management rules so they can hunt and kill the black-headed uakaris who live there.If the species’ survival is to be
ensured, further research into its ecology and tough anti-hunting measures, including legislation and enforcement, must occur.
Our thanks to Bruna Bezerra, PhD, of the University of Bristol School of Biological Sciences for providing and allowing our use of her beautiful photos of the black-headed uakari.
Written by Kathleen Downey, August 2017