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Cacajao melanocephalusblack uakari

By Paul Morse

Geographic Range

Cacajao melanocephalus is known from blackwater rivers in the northern, interior Amazonian basin. The two subspecies (C. m. melanocephalus and C. m. ouakary) together occupy a distribution throughout southeastern Colombia, southern Venezuela and northwestern Brazil. Cacajao melanocephalus inhabits the forested region surrounding the Rio Vaupes, the Rio Japuro, as well as the Rio Negro river - with this geographic feature recently becoming the marker of the boundary between the subspecies (see Boubli, 1993). Cacajao m. melanocephalus occurs to the north and east of the Rio Negro, while C. m. ouakary is found to the south and west. This boundary is less clear in Brazil. (Barnett, 2005; Boubli, 1993)

Habitat

Occupying the upper Amazon basin, C. melanocephalus lives in forested habitats along blackwater rivers, principally the Rio Negro and several of its tributaries. This region is subject to seasonal rains and flooding, resulting in wet and dry seasons. Floods and annual inundation result in igapo forests along the banks of blackwater rivers, and these have long been the premiere sighting locations of these animals. Cacajao melanocephalus ouakary has yet to be sighted in terra firme forest at a distance greater than 200 meters from flooded igapo forests, restricting the known range of this subspecies to fluvial wetland forests. (Barnett, et al., 2005; Barnett, 2005)

The sighting of C. m. melanocephalus in terra firme forest by Boubli (1993) expanded both the geographic extent and habitat range for the species. These sightings have all occurred within Pico de Neblina National Park, Brazil. Long term studies in this site have confirmed that several of these groups live in non-flooded caatinga forest year-round. It has been suggested by Ayres (1989) that C. m. melanocephalus occupies the dry forest niche that is elsewhere filled by Chiropotes species (Boubli, 1993). Ayres and Clutton-Brock (1992) remark on the strangeness of Cacajao species being largely confined to igapo forests - effectively limiting their habitat ranges. This contrasts with their general finding that Amazonian monkey species capable of occupying fluvial forest tend to have larger geographic ranges than those species who are restricted to terra firme alone. (Ayres and Clutton-Brock, 1992; Barnett, 2005; Boubli, 1993)

Physical Description

Cacajao melanocephalus has a 2/2; 1/1; 3/3; 3/3 dental formula. Cacajao species are the largest of the pitheciines. They have short tails relative to their body size, with a tail length less than 50% of combined head and body length. Their tails are not prehensile. C. melanocephalus is further divided into two subspecies: C. m. ouakary is distinguished by a golden or yellowish mid-dorsum and nape from C. m. melanocephalus in which these body regions are reddish brown to black (alternate descriptions of coloration in C. m. melanocephalus may indicate a third, as yet undescribed, subspecies). (Barnett, 2005; Boubli, 1993; Fleagle, 1999)

The face of C. melanocephalus is black and naked, hence the common name "black-faced uakari" or "black uakari." Hands and lower limbs are also black. The rest of the animal is a deep brown color, except those regions mentioned above that distinguish subspecies. There is limited sexual dichromatism. The mandible is deep and particularly robust at the symphysis region. Although their canines have been known to reach 14 mm in length, they, like the incisors, are an important dietary specialization, allowing them to eat hard fruits and seeds with thick husks, and do not represent an instance of sexual dimorphism or play a role in sexual displays. (Ayres, 1989; Barnett, 2005)

  • Sexual Dimorphism
  • male larger
  • Range mass
    2.5 to 3.7 kg
    5.51 to 8.15 lb
  • Range length
    365 to 485 mm
    14.37 to 19.09 in

Reproduction

Due to the limited number of longitudinal studies on black uakaris, little is known about their mating behavior. Generally, Cacajao species live in large multimale - multifemale groups. These groups range from twenty to over a hundred individuals, making it possible that there are competitive mating strategies and that social hierarchy plays a role in mating opportunities. However, the lack of the major markers of sexual dimorphism such as large male canine size, the presence of sagittal or nuchal crests, or flamboyant colorings suggests that this species is largely monogamous, as is its sister taxon Cacajao calvus. (Barnett, 2005; Fleagle, 1999; Lindenfors, 2002)

Breeding appears to be seasonal, as young infants and lactating females have been observed only in the months of March and April, corresponding with the setting of fruit in igapo forests. Females give birth to single offspring. Infants receive care for some months, including being carried on the backs of parents in the months of June and July, when water levels are at their highest. Black uakaris have never successfully bred in captivity, so little is known of the specifics of breeding season or interval, gestation, or the development of infants and juveniles. In the more well-studied sister taxon C. calvus, the age of sexual maturity for females is approximately 43 months, with first pregnancy occurring soon thereafter. The offspring of C. calvus are weaned after approximately 550 days. The adult body size of C. melanocephalus is slightly smaller than that of C. calvus, thus the lengths of time for these life-history features in C. melanocephalus may be somewhat shorter. (Barnett, 2005; Lindenfors, 2002)

  • Breeding interval
    Breeding intervals are not known in black uakaris.
  • Breeding season
    Breeding appears to be seasonal, as young infants and lactating females have been observed in the months of March and April.
  • Range number of offspring
    1 (high)
  • Average number of offspring
    1
    AnAge

A typical primate trait is extended postnatal care of young. This has also been observed in black uakaris, where adults carry infants on their backs during the months of June and July when flood waters are particularly high. Little is known of the specifics of C. melanocephalus parental investment, as they have never bred in captivity and there is limited longitudinal data on this species. However, C. calvus exhibits extended parental care, including long term lactation. (Barnett, 2005)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • male
      • female
  • pre-independence
    • protecting
      • male
      • female
  • extended period of juvenile learning

Lifespan/Longevity

The lifespan of C. melanocephalus is not known from captivity or the wild. The lifespan of the closely related species C. calvus in the wild is about twenty years, which is a likely estimate in age for C. melanocephalus based on the many genetic and environmental similarities between these species (which suggest a similar life history as well as similar sources of extraneous mortality). (Lindenfors, 2002)

Behavior

Cacajao melanocephalus is a highly social species, living commonly in multimale-multifemale groups of twenty to thirty individuals, with some authors suggesting that groups can grow to over one hundred individuals. In one long-term study of C. m. melanocephalus, Boubli reported no observations of aggressive behavior between animals (unpublished thesis, see Barnett, 2005). Reports that the native Yanomame people keep young Cacajao as pets further suggests that they are generally social animals. (Barnett, 2005; Fleagle, 1999)

Home Range

The home range of C. melanocephalus is dictated largely by resource availability. The broad dispersal of food resources in igapo habitats means that large groups split into foraging parties of 3 to 10 individuals. The exact home range of C. melanocephalus is not known, although studies on Cacajao calvus have shown home ranges up to 550 ha, with the majority of activity (nearly 90%) restricted to a territory of 300 ha or less. It is reasonable to assume that the home range of C. melanocephalus is of equal or greater size when considering the similarity of habitats and the fact that C. melanocephalus has been observed to leave igapo forests for short times for distances of several kilometers to obtain food resources during seasons of particularly low availability. Analyses of population size and home range use suggest a density of about 20 individuals per square kilometer, though these analyses may be affected by seasonal observation of C. melanocephalus. (Ayres, 1989; Barnett, et al., 2005; Boubli, 1993; Fleagle, 1999)

Communication and Perception

Cacajao melanocephalus exhibits the typical primate characteristics of having a well-developed and specialized visual system and a reduced olfactory system. Visual and auditory perception are the most common and important long-distance forms of perception, though tactile perception remains significant. The main types of communication observed among black uakaris are those that occur between foraging groups, which serve to hold the group together or to warn of predators. These are mostly auditory signals such as the intergroup contact calls: "keek" or "chick". The warning call is a distinctive two-syllable cry: "bi-koh." These calls are surely important for a species that is constantly on the move for food resources in a rich, complex, three-dimensional environment, especially if large groups divide into smaller foraging groups during the day, as has been suggested. Additional verbal communication occurs between juveniles at play, who emit a hissing noise. (Barnett, 2005)

Tail-wagging is an additional form of communication, which has been observed to occur constantly during group calls in C. m. melanocephalus. In C. m. ouakary tail-wagging has only been associated with threat displays initiated upon first contact of the group with humans. (Barnett, 2005)

Food Habits

The diet of black uakaris is relatively broad, including insects and various plant materials. Cacajao species are known for being specialized feeders that focus mainly on immature fruits and seeds. This specialized feeding has led to adaptations in cranio-dental morphology, as well as habitat specificity. Feeding is generally accomplished by hind limb suspension. (Barnett, 2005; Fleagle, 1999; Rosenberger, 1992)

Although frugivory is common in primates, consumption of unripe fruits and granivory are both rather unusual. Among New World monkeys, this rather restricted diet is exploited by members of the subfamily Pitheciinae; typically by the more widespread and well-known Chiropotes species. Ayres (1989) speculated that C. melanocephalus fills this dietary niche in igapo forests and restricted terra firme forest that is elsewhere filled by Chiropotes (Boubli, 1993). This dietary specialization explains many of the physical adaptations seen in black uakaris. Particularly their procumbent incisors, deep mandibular symphysis, and tusk-like but non-sexually dimorphic canines represent dental adaptations to remove seed resources from the tough husks of unripe fruits or hard shells. The distribution of seeds in igapo forests and between wet and dry seasons is cited as an explanation for the tendency of black uakaris to break into smaller groups for daily foraging, as well as for the high occurrence of inter-group communication. (Ayres, 1989; Boubli, 1993; Fleagle, 1999)

Observations of the feeding habits of black uakaris suggest that over 50% of the diet is comprised of unripe seeds. The most common seed type is from the pods of Inga laurina. During the dry season, when seeds and fruit become rare, their diet shifts to include leaves and some insects. They take young leaves from Buchenavia oxicarpa and Eschweilera tenuifolia, or older leaves of Mabea taquari to avoid the toxic levels of latex in young leaves of this species. Insect consumption includes passive insectivory that occurs during fruit consumption and also the predation of Polistes wasp larvae during dry seasons when fruits and seeds are not available. A more detailed description of dietary components can be found in Barnett et al. (2005). (Ayres, 1989; Barnett, et al., 2005)

  • Animal Foods
  • insects
  • Plant Foods
  • leaves
  • seeds, grains, and nuts
  • fruit
  • nectar
  • flowers

Predation

The only known predators of black uakaris are humans. Adults are rarely hunted as food by local tribes such as the Yanomame. However, observational data suggests that an aerial predator may be a significant source of mortality for C. melanocephalus, as warning calls are initiated even when non-carnivorous large birds are sighted. It is probable that birds of prey such as hawks or eagles can easily threaten young and adults. (Barnett, 2005)

Ecosystem Roles

No description yet exists of any species commensal with C. melanocephalus. Primates are generally parasitized by a number of ecto and endoparasites. Observations on C. calvus participating in grooming behavior suggest uakaris do have external parasites. Specializing in the consumption of fruits with hard husks and immature seeds, C. melanocephalus does not have a beneficial role for these plants. It is most accurately considered a seed predator (Barnett, 2005). (Ayres, 1989; Barnett, 2005; Fleagle, 1999)

Economic Importance for Humans: Positive

Because of their limited contact with people, black uakaris are not known to provide benefits to humans outside of their role in healthy Amazonian ecosystems. On rare occasions they are a food source for local people. There are also several accounts of locals taking young for pets. (Barnett, 2005)

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

There are no known adverse effects of C. melanocephalus on humans, particularly due to their limited contact with humans.

Conservation Status

The conservation status of C. melanocephalus is not fully understood. Confusion can be seen in the designations listed below by different endangered species databases. The "endangered" status listed by the US Federal government reflects an older classification of the species, dating from 1970. The IUCN Red List recognizes a more recent argument from 1996 that C. melanocephalus is at lower risk. However, researchers (quoted in Barnett, 2005) are quick to point out that the restricted diet and habitat of C. melanocephalus could quickly lead to endangered status if those habitats are threatened. Others have expressed concern that the context in which researchers often observe these animals - during seasons in which the igapo is in high flood stage and when food sources are widely available - has given a false impression of the total number of black uakaris. There is currently no plan in place to protect the species or its habitat. (Barnett, 2005)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Paul Morse (author), Yale University, Eric Sargis (editor, instructor), Yale University.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

frugivore

an animal that mainly eats fruit

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Ayres, J. 1989. Comparative Feeding Ecology of the Uakari and Bearded Saki, Cacajao and Chiropotes . Journal of Human Evolution, 18: 697-716.

Ayres, J., T. Clutton-Brock. 1992. River Boundries and Species Range Size in Amazonian Primates. The American Naturalist, Vol. 140, No. 3: 531-537.

Barnett, A. 2005. Cacajao melanocephalus. Mammalian Species, No. 776: 1-6.

Barnett, A., C. Volkmar de Castilho, R. Shapley, A. Anicacio. 2005. Diet, Habitat Selection and Natural History of Cacajao melanocephalus ouakary in Jau National Park, Brazil. International Journal of Primatology, Vol. 26, No. 4: 949-969.

Boubli, J. 1993. Southern Expansion of the Geographical Distribution of Cacajao melanocephalus melanocephalus . International Journal of Primatology, Vol. 14, No. 6: 933-937.

Fleagle, J. 1999. Primate Adaptation and Evolution, Second Edition. United States of America: Elsevier (USA).

Lindenfors, P. 2002. Sexually antagonistic selection on primate size. Journal of Evolutionary Biology, Vol. 15, No. 4: 595 - 607.

Rosenberger, A. 1992. Evolution of Feeding Niches in New World Monkeys. American Journal of Physical Anthropology, 88: 525-562.

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