BROWN-HEADED SPIDER MONKEY
Geographic Distribution and Habitat
The brown-headed spider monkey (Ateles fusciceps), also known as the black-headed spider monkey, is native to the South American countries of Colombia, Ecuador, and Panama. They live in humid tropical and subtropical forests up to an elevation of 8,200 feet (2,500 m) above sea level or in lowland tropical rainforests. In some places, they may live in the edges of forests near agricultural areas. They occupy the largest range of forest habitats of any of the Colombian spider monkeys.
There are two subspecies of brown-headed spider monkeys: A. fusciceps fusciceps, which uses the common name “brown-headed spider monkey,” and A. fusciceps rufiventris, which goes by the common name “Colombian spider monkey.” The brown-headed spider monkey subspecies is limited to northwestern Ecuador and possibly parts of southern Colombia. Colombian spider monkeys range from western Colombia to eastern Panama. Some authorities do not recognize brown-headed spider monkeys as a distinct species, rather considering them a subspecies of Geoffroy’s spider monkey (Ateles geoffroyi).
Size, Weight, and Lifespan
Females weigh about 18 lbs (8 kg) on average. Males are slightly larger at an average weight of about 20 lbs (9 kg). Their head and body length is about 16–22 inches (40–55 cm) on average with an impressively long tail of about 28–34 inches (70–85 cm). They live to about the age of 25.
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, members are likely to compete for access to limited resources and mating opportunities.
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Brown-headed spider monkeys possess the exaggerated, almost cartoonish, body proportions characteristic of all spider monkeys. They have extremely long arms and legs that give them a gangly, wiry appearance. Their limb length is exaggerated by a relatively small head atop their shoulders. However, these long limbs, as well as their long and fully prehensile tails, allow them to move quickly and agilely in the highest part of the canopy. Their tail is hairless and ridged on the bottom to allow them better grip strength. Indeed, they can easily support their entire body weight on their tail and frequently use it as a fifth limb!
Their hair is long and wiry, providing them the necessary warmth for what can often be cold nights in the canopy. The hair on their heads is swept forward, resembling what looks to be a punk-like hairstyle. The brown-headed spider monkey subspecies is brownish-black, while the Colombian spider monkey subspecies is all black. A layperson seeing a group of brown-headed spider monkeys for the first time may confuse the males with the females. Curiously, females are the ones with the most obvious external genitalia: they possess what’s known as a “pendulous clitoris” that is actually larger than the male’s penis. The organ may help males to more easily pick up on chemical cues of the female’s reproductive status.
Brown-headed spider monkeys possess a few unique evolutionary adaptations that allow them to thrive in their high canopy habitat. Curiously, they do not have thumbs, just four fingers on each hand. Although their ancestors had thumbs, spider monkeys do not have much use for them considering that they primarily move by swinging and hanging. Thumbs may have even inhibited this movement, causing the thumbs to become vestigial over time and eventually lost altogether. Their feet, however, possess opposable toes that allow them to grip branches. Baseball pitchers or tennis players would be very jealous of spider monkeys’ shoulders—they have incredibly mobile shoulder joints that allow the monkeys a very full range of motion.
Brown-headed spider monkeys are mostly frugivorous, meaning that their diet is mostly composed of fruit. Mature, soft fruit found in the upper canopy comprises about 83% of the diet. They supplement their diet with young leaves and flowers, seeds, floral buds, bark, decaying wood, and even honey. They eat more of these supplemental foods during times of fruit shortages. Every once in a while they may opportunistically feed on termites, caterpillars, or eggs. One of the favorite fruits of brown-headed spider monkeys is that of the Brosimum utile tree.
Behavior and Lifestyle
Brown-headed spider monkeys are most at home in the high canopy, where they spend most of their time. They may dip down into the middle or lower canopy, but they are almost never found in the understory of the forest. They are highly suspensory, meaning that they spend much of their time hanging from branches. They move about via climbing and brachiation—swinging from branch to branch with their long arms. Believe it or not, they are able to cross a 30-foot (9 m) gap between branches! They may also hang from underneath a branch and use their hands and feet to “walk” along it, while suspended upside down. They rarely walk or run on all fours, at least not right-side up.
Brown-headed spider monkeys are known to have excellent memories. They are able to remember complex routes taken through the canopy to find food and can remember exactly which trees bear fruit and when.
Brown-headed spider monkeys live in fission-fusion social groups, in which one large main group splits into smaller subgroups to forage. The subgroups, which are often composed of a mother and her offspring, usually reconvene after foraging, although sometimes a subgroup may sleep apart from the main group. A typical main group is composed of about 20 individuals, with subgroups of between about 1–10 individuals. The groups are matriarchal, with females in charge and males responsible for defending the territory. Each sex has its own well-defined dominance hierarchy.
Brown-headed spider monkeys make a wide variety of vocalizations. Physical touch is an important method of communication within their groups. They are known to embrace and cuddle frequently with groupmates. Embraces are especially common when subgroups reunite after foraging. Olfactory communication is important for brown-headed spider monkeys, as evidenced by the scent gland that males possess on their chests.
Female brown-headed spider monkeys indicate that they are ready to mate through body language and scent changes. A female is ready to mate about every 26 days. When she finds a willing partner, she stays close by him for about three days, copulating multiple times. Their gestation length is 7.5 months, after which a single infant is born. Brown-headed spider monkeys are usually born in the rainy season. They are born mostly bald, although their black fur comes in by about three months of age. They are cared for solely by their mother, who carries her baby on her belly for about four months, then on her back. She nurses her baby for a full 20 months. Males usually stay in the natal group, while females leave their natal group upon reaching sexual maturity at five or six years of age.
Brown-headed spider monkeys are important seed dispersers. A study of a closely related species, the red-faced spider monkey (A. paniscus), found that they disperse the seeds of 138 tree species through defecation and another 10 species by carrying the fruit away from the tree and dropping it. Only 23 species of the fruit they consumed were not dispersed. Brown-headed spider monkeys are predated by jaguars, pumas, ocelots, and large snakes.
The International Union for Conservation of Nature lists brown-headed spider monkeys as Endangered (IUCN, 2020), appearing on the IUCN Red List of Threatened Species. This assessment is based on an expected population loss of more than 50% over the next 45 years or three generations. This has led to their being widely considered the most endangered primates in Ecuador. The major threats that brown-headed spider monkeys face are habitat loss and fragmentation, hunting, and collection for the pet trade.
Forest data suggest that by 2063, almost 20% of brown-headed spider monkey habitat is likely to be lost. Over 30% of the habitat in Colombia along the Caribbean coast has been lost in the past 10 years. Only 2.5% of secondary habitat is left in this region. Habitat fragmentation is another serious issue. Fragmentation is the loss of connections between different patches of habitat. Oftentimes, the monkeys find themselves in isolated “islands” of forest, unable to cross the heavily altered, not to mention dangerous, landscape to find new habitat. This leaves the monkeys reliant on whatever food sources happen to be in their fragmented forest and genetically isolated from other populations of brown-headed spider monkeys.
To exacerbate these issues, the monkeys are hunted as a protein resource for indigenous people in their range, and sometimes for their pelt. With their populations dwindling from habitat loss, this adds an additional strain. Spider monkeys are also sometimes kept, unwisely, as pets, and there is an additional threat from the pet trade when brown-headed spider monkeys are collected from the wild.
Brown-headed spider monkeys are listed in Appendix II 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. They are considered Critically Endangered in the Red Book of Mammals of Ecuador and appear on the IUCN’s list of the world’s 25 most threatened primate species. The species is protected under Ecuadorian law that prohibits hunting and commercialization of the animals and is listed as Critically Endangered under Panamanian law.
In areas where threats are reduced, the brown-headed spider monkey population has increased, showing that conservation actions work. For example, in Esmeraldas, Ecuador, hunting of the monkeys was stopped and their population has begun to recover. Conservationists recommend protection areas of lowland forests where population densities of brown-headed spider monkeys are high, the habitat quality is good, and hunting pressure is low. It has also been recommended to protect corridors of habitat between isolated patches of forest, which would allow the animals to move more freely and increase gene flow. Other recommended conservation actions include creating national education campaigns to prevent illegal trade, the establishment of breeding programs in zoos and rescue centers for reintroduction, and researching the distribution of brown-headed spider monkeys to better understand their range.
There are several priority areas for the conservation of brown-headed spider monkeys, including the Cotacachi-Cayapas Ecological Reserve, Corredor Awacachi, the Awa Ethnic Forest Reserve, and the buffer areas around these reserves. While brown-headed spider monkeys occur in national parks, these parks are believed to have very low populations of spider monkeys because of hunting pressure.
- Collins, A. 2008. The taxonomic status of spider monkeys in the twenty-first century. In C. Campbell (Ed.), Spider Monkeys: Behavior, Ecology and Evolution of the Genus Ateles (Cambridge Studies in Biological and Evolutionary Anthropology, pp. 50-78). Cambridge: Cambridge University Press. doi:10.1017/CBO9780511721915.003
- Schwitzer, C. et al. 2015. Primates in Peril: The World’s 25 Most Endangered Primates. IUCN SSC Primate Specialist Group and Conservation International. https://www.researchgate.net/publication/285322735_Ecuadorian_Brown-headed_Spider_Monkey_Ateles_fusciceps_fusciceps_Gray_1866_Ecuador_Colombia_20142016
Written by K. Clare Quinlan, October 2022