BROWN-HEADED SPIDER MONKEY

Ateles fusciceps

Geographic Distribution and Habitat
The brown-headed spider monkey is endemic to Ecuador, Colombia, and Panama. There are two known subspecies: the nominate brown-headed spider monkey, Ateles fusciceps fusciceps, found in the Andes tropical and subtropical humid forests of northwestern Ecuador, and the Colombian black spider monkey, Ateles fusciceps rufiventris, found in the dry, humid, and cloud forests of southwestern Colombia and in Panama. All live in forests at altitudes between 300 and 5,580 ft (100-1,700 m) above sea level.

Brown-headed spider monkey range map, courtesy of the IUCN, 2020

Size, Weight, and Lifespan
Spider monkeys are the largest of the New World monkeys. They are 16-22 in (40-55 cm) in length; their tail is longer than their body at 28-34 in (70-85 cm). Their average weight is 20 lbs (9 kg), with females being slightly larger than males.

Brown-headed spider monkeys can live up to 24 years in the wild, and longer in captivity.

Appearance
Brown-headed spider monkeys are quite elegant with their long limbs and slender body—especially when swinging and leaping from branch to branch in the canopy. Compared to their body, the head of a spider monkey looks small. Their eyes are usually a deep brown color and are full of expression. Their mouth is narrow with thin brown lips, and their flat noses have triangular nostrils. Their ears are black and large and look very much like a human’s. The body and head of brown-headed spider monkeys are entirely brown; the body and head of Colombian black spider monkey subspecies are black with a few white strands on the chin.

Their coats are thick, long, shaggy, and a little rough to the touch, and the hair on their head always seem to be brushed forward, giving them a somewhat punk-ish style. Their thick coat provides much-needed coverage during the cold nights in the canopy.

The underside of their prehensile tail is hairless with ridges for gripping, while the outside is covered in fur. It is strong enough to support their body weight and is used as a fifth limb. Their hands, which lack thumbs, have four long fingers—not great to manipulate objects or food items, but perfect for brachiation, which is how these monkeys move about most of the time. With opposable toes, their feet are perfectly designed to grab and hold onto branches while climbing trees.

What Does It Mean?

Activity Budget:
A way to quantify animal behavior by observing an animal over an extended period and documenting activity. An activity budget demonstrates how much time an animal spends in various activities such as eating, resting, sleeping, and moving.

Agonistic:
Of, relating to, or being aggressive or defensive social interaction (such as fighting, fleeing, or submitting) between individuals usually of the same species.

Alarm call:
Specific calls that individuals in a troop make to warn other members of their group of imminent danger, such as predators.

Brachiation:
Also called arm swinging, this is a form of arboreal locomotion in which primates swing from tree limb to tree limb using only their arms.

Fission-fusion society:
A society in which the members of a social group break off into smaller groups and then rejoin as a larger group.

Nominate subspecies:
In zoological nomenclature, when a species is split into subspecies, the originally described population is retained as the “nominotypical subspecies,” which repeats the same name as the species.

Prehensile:
Able to grasp or hold objects.

Quadrupedal:
Using four limbs/legs to locomote. This word comes from the Latin meaning “four feet.”

Visit the Glossary for more definitions

Diet
Mostly frugivorous, these monkeys eat the mature, soft part of a wide variety of fruit (up to 80% of their diet), often from timber trees. Other commonly found items on their menu are young leaves (up to 20% of their diet) and flowers, seeds, floral buds, aerial roots, bark, decaying wood, and honey, as well as the occasional termite or caterpillar.

Behavior and Lifestyle
Brown-headed spider monkeys live in groups composed of 20-30 individuals. They live in a fission-fusion society—i.e., the group breaks down in smaller units of 2-4 individuals, usually a mother and her offspring—and disperse during the day for foraging. At night, the entire group gets back together.

They travel and forage in the canopy and occasionally use the middle and lower strata of the forest, but do not spend any time in the understory. They travel by climbing and swinging from branch to branch, a mode of locomotion known as brachiation. When leaping, their arms are generally fully extended for maximum reach and they are able to leap in excess of 30 ft (9 m) between trees. They occasionally walk on two feet or run on all fours. When in a quadrupedal position, 70% of their body weight rests on their hind limbs.

They have a great ability to map out the forest as they move from one foraging site to another, so they know exactly which tree is bearing fruit where and when.

Daily Life and Group Dynamics 
Males usually stay in their natal group; females move and join other groups. Females form affiliations based on shared life stages—for instance, mothers with offspring in a similar age group tend to hang out together and let their young interact. As their progenies grow older, they do not remain as close as they once were and may associate with other females.

Grooming, which accounts for 5% of the time budget in the day of a spider monkey, is the glue that holds the group together. Mothers tend to give more grooming than they receive.

Spider monkeys embrace and hug each other, particularly juveniles with adult males. This behavior is observed more in captivity than in the wild. Between males especially, the embrace may be preceded by genital presentation and sniffing—this all part of the social bonding experience.

Spider monkeys have pectoral and sternum glands, which they rub on branches to mark their territory (or to relieve an itch) and send messages to other individuals in the group. They also like to rub fragrant things, such as food, on their chest. This behavior is not believed to function as a way to repel insects or parasites, even though this is the case in other primate species.

Fun Facts

The species name “Ateles” derives from a Greek word, “atéleia,” which means incomplete or imperfect. It was probably chosen because they don’t have a thumb.

Spider monkeys are called “spider” monkeys because they are said to look like spiders when when they hang from a tree suspended by their tails.

​All spider monkeys see in color—which is useful for foraging and detecting the ripest fruit—but cannot detect the color blue. How they perceive green, yellow, and red differs slightly according to the species.

Communication
Like all primates, brown-headed spider monkeys have many ways to communicate with their peers, including visual displays, vocalizations, and olfactory cues.

Spider monkeys greet each other with their chin up. Brief “tee-tee” or “whinny” sounds may be uttered at that time. While foraging, quick repeated calls are used to tell other members of the community where a desirable food item is located.

Males are more likely than females to engage in impressive agonistic displays. The aggressor, with his hair up and mouth open, leaps down at dizzying speed, while staring with hostility at a targeted individual. Note that direct eye contact, teeth exposure, yawning, and staring are always threats, as well as coughing and growling. Usually, the threatened spider monkey leaves the scene screaming and tries to remain as far as possible from the attacker, sitting with his head buried in his knees.

Juveniles can be seen grappling—one may approach and hang above the other, extending a hand while shaking his head and uttering ook-ook vocalizations, which are always associated with play fighting. The two then start mock biting and wrestling.

Following a frightening event, some individuals may embrace, then sit or walk with their tails wrapped around each other.

Teasing is not uncommon. One spider monkey may pull the tail or hair of another, which causes the latter to react with a tense grin (mouth retracted and teeth slightly exposed).

Spider monkeys can be noisy; low frequency repetitive barks, accompanied or not by piloerection, urination, and defecation, are used to alert others of danger. Shaking branches can be used to scare away the threat. High pitched, repetitive trills and twitters, on the other hand, are heard when the group is excited, but not necessarily at risk.

Long calls are used to gather the group together and adult males sometime utter “caw” calls (three successive roar-like vocalizations) to gather the females around.

Reproduction and Family
Brown-headed spider monkeys become sexually mature at about 4 years old and can mate all year long. It is easy to recognize females as their clitoris is elongated and protrudes out.

Receptive females choose their partner and clearly communicate their readiness to mate. During the estrous cycle, which lasts 26 days, spider monkeys change behaviors: females groom more than normally and both genders scent-mark and sniff each other’s genitals. They also use visual signals—for instance, a female may approach an adult male and present.

Unlike many other primates, female spider monkeys do not show any physical signs of estrous. They don’t swell.

The gestation period lasts 230 days on average and the interbirth interval is 2 to 3 years, although if a baby is still-born, the female can get pregnant again about 8-9 months later.

Babies weigh approximately 400 grams (under 1 lb) and are born black; they get their adult coloration after they are done nursing. Females give birth to one offspring.

The mother carries her infant around her stomach for the first 4-5 months of life. The baby can hold on to her by grabbing the two tufts of hair on the side of her body. Despite careful mothering, infant mortality is high due to falls. After 5 months, the mother carries the baby on her back. The young are breast fed for 16 months; they add solid food to their diet at 8 months old. The youngsters may pout their lips to tell their moms they want some comfort. When it is time for them to be weaned, mothers may withdraw from suckling and a distraught juvenile may look at her, mouth partially open while uttering twitter calls.

Although they don’t really get involved in the rearing of their offspring, males allow youngsters to ride on their backs before they are fully independent. They do not carry infants, however. Males can also be seen embracing and holding a tweeting and screeching juvenile who has been recently punished by her mother.

Photocredit: Patrick Muller/Creative Commons

Ecological Role
Like all forest dwelling primates, brown-headed spider monkeys play an important role as seed dispersers. The timber fruit they consume cannot germinate until the outer layer of the seeds have softened, which occurs as they pass through the monkey’s digestive system. This allows many tree species to propagate. Foraging activity also stimulates the growth of trees, since extra foliage, branches, and other organic matter that is dropped from the canopy provides nutrients to the soil. Their feces are rich in nitrogen and phosphorus as well.

Conservation Status and Threats
The brown-headed spider monkey is classified as Endangered on the International Union for Conservation of Nature Red List (IUCN, 2020). Their population is estimated to have decreased by 80% over the last few decades and recent satellite pictures show over 30% habitat loss on the Atlantic coast of Colombia alone.

Habitat fragmentation due to intensive logging activity and agriculture, as well as human population growth, constitute major threats to the survival of the brown-headed spider monkey—not to mention hunting for food and fur, which adds a lot of pressure on the species. The proximity of their home range to agro-ecosystems may expose these primates to parasites and pathogens they would not normally encounter. Long inter-birth intervals and a high infant mortality rate are also contributing factors to their decreasing numbers.

In Panama, the Colombian black spider monkey (A.f. rufiventris) subspecies is Critically Endangered due to deforestation and heavy hunting activity as indigenous people use them as a cultural protein resource. Adding to the problem is uncontrolled deforestation. The Chucantí Nature Reserve is one of the few areas in the Darien Province that are now protected by the land owner. 

The primary predators of spider monkeys are jaguars, pumas, ocelots, large snakes, and humans.

Conservation Efforts
The Tesoro Escondido cooperative, located in the Canande watershed within the Cotacachi-Cayapas Ecological Reserve in northwestern Ecuador, is a crucial area for the survival of the brown-headed spider monkeys. Studies conducted in this area focus on the importance of the “matrix” rather than on habitat fragmentation and its ill-effects. The “matrix” is made of areas surrounding native forest strips. The landscape in this region is a mosaic of cattle pastures, cacao agro-forests, tree plantations, and patches of tropical moist forest. Settlers arrived in the 1920s; today all land, including forests, is privately owned.

The area is home to several brown-headed spider monkey groups that live at altitudes under 2,000 ft (600 m) with temperatures averaging 73F (23C). Humidity is rather elevated, due to summer fog. The species seems to be present at two specific sites: Awá Indigenous Reserve (AIR) and Cotcachi-Cayapas Ecological Reserve (CCER). Brown-headed spider monkeys went extinct in the Manabí province in the 1950s. The mere presence of brown-headed spider monkeys in a highly fragmented habitat is encouraging. It indicates that these primates can travel through the agricultural matrix and survive, hence the importance of promoting the plantation of native vegetation corridors and shade trees to allow for their dispersal, while simultaneously contributing to farmers’ livelihoods.

There are several noteworthy conservation programs. Ecuador’s Ministry of Environment Socio Bosque project is one of them. Started in 2008, it offers economic incentives to forest owners who agree to protect biodiversity. Proyecto Washu, which ensures the protection of the brown-headed spider monkeys, is another great example. It provides research and environmental education, and contributes to enhancing local community life by promoting organic cacao production as an alternative to deforestation.

In Ecuador, the brown-headed spider monkeys are protected in accordance with Resolution No. 105 of the Ministry of the Environment, which prohibits hunting and commercialization in the country.

There are designated protected areas for both subspecies: Cotacachi-Cayapas Ecological Reserve, Los Cedros Protected Forest, and Awá Ethnological Reserve for brown-headed spider monkeys, Ateles fusciceps fusciceps; Los Katios Natural National Park and Las Orquideas Natural National Park for Colombian black spider monkeys, Ateles fusciceps rufiventris.

The species is listed in Appendix II of The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).

References:

  • New population and range extension of the Critically Endangered Ecuadorian brown-headed spider monkey (Ateles fusciceps fusciceps) in western Ecuador – Laura Cervera and Daniel M. Griffith​
  • Canopy – Journal of the Primate Conservation MSc Programme – Oxford Brookes University – “Modelling occupancy for the Critically Endangered brown-headed spider monkey (Ateles fusciceps fusciceps) in Tesoro Escondido NW Ecuador – Denise Spaan
  • Agroecosystems and Primate Conservation in The Tropics: A Review – Alejandro Estrada, Becky E. Raboy and Leonardo C. Oliveira.
  • Smithsonian Contributions to Zoology – number 213 – “Communication Mechanisms and Social Integration in the Black Spider Monkey, Ateles fusciceps robustus, and Related Species” – John F. Eisenberg 
  • Enrichment for Colombian black spider monkeys (Ateles fusciceps rufiventris) in a zoo – Tina Torstensson
  • American Journal of Physical Anthropology 143-188-197 (2010) – Monkeys and Apes: Are Their Cognitive Skills Really So Different? – Federica Amici, Filippo Aureli, Joseph Call
  • Tesoro Reserve Organization website
  • Action for the Wild Organization website
  • IUCN Red List

Written by Sylvie Abrams, July 2018. Conservation status updated July 2020.