Geographic Distribution and Habitat
The Goeldi’s monkey (Callimico goeldii), also known as the Goeldi’s marmoset, the Goeldi’s tamarin, or callimico, is a member of the Callitrichidae family. Endemic to South America, this evasive and shy “mystery monkey” is dispersed throughout the upper Amazonian rainforests in localized, but fragmented groups. Suspected population decline and secretive behavior make it difficult for researchers to observe them for extended periods of time.
Although their splintered distribution makes it difficult to pinpoint their exact territory, they are known to inhabit southern Colombia, western Brazil, northern Bolivia, and eastern Peru. Two major rivers, the Rio Caqueta in Colombia and the Rio Manuripi in Bolivia, serve as the northern and southern borders of their geographic distribution. From east to west, researchers have estimated populations are contained between the Andean foothills in Peru and the Rondonia region of Brazil—however, the exact cut-off is unknown.
This diminutive species prefers the dense understory of primary forests based on the availability of their seasonal keystone food groups: fruits and mushrooms. Groups have been known to change their habitats based on the wet or dry seasons, and settle throughout bamboo forests, varillales (white sand forests with thin trees), open mature forests, and disturbed forests.
Goeldi’s monkeys were first described in 1904 and are monotypic, or the only species of their genus, Callimico. They are named after the Swiss zoologist, Emil August Goeldi, a professor who worked in South America. They are distinguished from other members of the Callitrichidae family (consisting of tamarins and marmosets) by having three molars instead of two and birthing single infants instead of twins.
Size, Weight, and Lifespan
These small primates are only slightly larger than a squirrel and display a faint level of sexual dimorphism. Males weigh 12 ounces (366 g) while females are a touch heavier at 12.5 ounces (355 g). They are also a little bit longer. Average height is 7.5–9 inches (19–23 cm) long. Their non-prehensile tails (meaning they’re unable to grasp things with it) are 10–13 inches (25.5–32.4 cm) long.
In captivity, individuals weigh 1–1.3 pounds (454–590 g). Sometimes, individuals in captivity are larger than their wild counterparts because of regular feeding and medical care. They may also experience less physical activity since they do not have to rely on daily travel and foraging for their meals.
The oldest known Goeldi’s monkey lived to be 22 years old in captivity. In the wild, life expectancy is around 10 years.
Don’t let their size fool you—these small primates have a lot of charisma and poise packed into their small stature.
Their bodies are compact with muscular legs that offer remarkable power, making them impressive little leapers. They are covered in soft, dense fur—most commonly black, but also shades of black-brown, brown, gray, and even reddish-brown. Their silky, shaggy coat covers almost all of their body. A heavier cape of fur drapes around their head and shoulders that, depending on the individual, offers a sense of regality … or wildness! Lighter highlights may steak across the crown of their heads or along their torso. They have rounded, dark, hairless faces and large, expressive eyes ranging from amber to dark brown. Their muzzles bear a pug-like nose and a long, wide mouth. Tails are long and non-prehensile, sometimes donned with faint, hued rings at the base.
Goeldi’s monkeys have claw-like nails, except for a singular “toilet” or “grooming” claw, known as a hallux, on the second toe of each foot. Like all claws and nails, it is made of keratin. It is a specialized claw, common in many primates, used for grooming, raking through fur, clinging to branches, scansorial (climbing) travel, and procuring food from trees.
Goeldi’s monkeys are omnivores and experience seasonal variations in their diets. During the wet season, fruit is their primary source of nourishment. In January and February, Goeldi’s monkeys will break from their usual elevation and ascend the tree canopy to pick ripe, juicy offerings.
During the dry season, they alter their consumption and indulge in copious amounts of fungi. In fact, there are very few primates who fortify their diet with as many mushrooms as they do. From May to July, fungi account for 48–63% of their diet. Many researchers believe this adaptation developed to avoid food competition. Goeldi’s monkeys will search along streams and throughout bamboo thickets, fallen trees, and rotting wood to find delectable jelly and bamboo fungi.
Nourishment is also sourced from a variety of nectar, plants, gums, insects, and larvae, as well as spiders, cicadas, mantids, moths, cockroaches, bird eggs, small vertebrates, scorpions, lizards, frogs, and toads.
Behavior and Lifestyle
Considered “understory specialists,” Goeldi’s monkeys are arboreal and diurnal, effectively canvassing the canopies of the rainforest by day and sleeping by night.
They are recognized as the strongest leapers of all callitrichids, and easily navigate trees, trunks, and lianas at comparatively lower heights. Their locomotion is typically horizontal and quadrupedal, consisting of walking, running, leaping, and hopping. A great deal of time is spent clinging to support branches. On occasion, they will vertically scale trees to reach higher-growing fruit, or to descend lower for terrestrial excursions (mainly for foraging).
During rest periods, they spend their time scanning, sitting, investigating, and partaking in social grooming.
Goeldi’s monkeys are phenomenal long jumpers—they can leap 13 feet (~4 m) horizontally without losing any height. To put it in perspective, it would be like a person leaping from one end of a tennis court to another in a single jump!
They are one of the few primates that predominantly consume mushrooms during the dry season when fruit is scarce.
Mothers, fathers, and older siblings help raise youngsters. To teach them independence, they will even steal their food away to teach them both to be self-sufficient and the need to forage.
Goeldi’s monkeys live in tight-knit family groups of six to eight and seldom drift more than 49 feet (15 m) away from each other. These groups consist of multi-male/multi-female individuals and include their offspring. They spend most of their time resting, traveling, grooming, and foraging. As collaborative caregivers, adults (both parental and non-parental) will share food with each other, juveniles, and infants.
They have a relatively large territory for their size, spanning from 740–1,975 acres (30–80 hectares). They prefer to remain in the lower canopy, 16.4 feet (5 m) off the ground. Each day, they travel an estimated 1.2 miles (2 km) in a circular pattern.
Goeldi’s monkeys travel in sympatry (a term for coexistence amongst other species) with saddleback tamarins (Leontocebus fuscicollis) and moustached tamarins (Saguinus mystax). These groups stay together to capitalize on foraging opportunities and avoid predation. At dusk, they separate and retreat to their own nests—dense tangles of vines, vegetation, and leaves—situated 32 feet (10 m) above the ground for a night’s rest.
It appears that Goeldi’s monkeys can get along with almost everybody. They have also been observed amongst groups of pygmy marmosets (Callithrix pygmaea), capuchins (Cebus albifrons, C. apella), squirrel monkeys (Saimiri boliviensis), titi monkeys (Plecturocebus brunneus, C. cupreus), red howler monkeys (Alouatta sara), owl monkeys (Aotus nigriceps), sakis (Pithecia irrorata), and emperor tamarins (Saguinus imperator).
Goeldi’s monkeys are a highly social species and have a diverse repertoire of communication techniques. Vocalizations, facial expressions, body language, and olfaction (scent) communication are all used to convey a variety of messages.
Up to 40 different vocalizations are used to communicate with each other, including long-distance contact calls, long-distance location calls, short-distance contact calls, short-distance location calls, alarm calls, warning calls, and agonistic calls. This collection is composed of whistles, chirps, screams, and twitters. Long-distance cries are slow, with a decrease in frequency towards the end. They sound like high-pitched whistles and can be monosyllabic or have a minute rhythm, traveling more than 328 feet (100 m). Short-distance calls consist of rapid bursts of clicking to find family members during movement or to communicate during feeding.
Alarm calls come in waves of three sweeps and warning calls are trill screeches. Agonistic calls have a wide variance based on the level of aggression.
Babies have a notable, whistle-like call for their first 3 months of life. They also have a “hoe hoe” contact call, and others for excitement, play, aggression, tense situations, and even maternal rejection.
Yawns sneak up on Goeldi’s monkeys during frequent rest periods, just like with humans. They use stares to threaten and challenge others, grimaces to display appeasement or submission, and tongue flicks to communicate an intense threat or to initiate copulation.
Body language can demonstrate an array of emotions and messages. Some postures are for grooming and mating. Aggression is displayed when individuals open their mouth wide, arch their posture, raise their hair (also known as piloerection), and begin “arch bristle leaping,” where they leap to and from support branches in an effort to appear big and intimidating so they can ward off potential threats.
Goeldi’s monkeys participate in genital marking and sternal (upper chest) rubbing for olfactory communication. They have a pronounced sternal gland specifically for this. This type of communication is used for mating, grooming, and identifying territory. Tail marking occurs when they urinate on their tails and rub it across their chest, torso, and genital area.
Mating season occurs from September to October (dry season) and April to May (wet season). While many speculate that Goeldi’s monkeys are monogamous, some studies suggest that this is more common in captivity and that wild populations can be polygamous.
Females initiate copulation, sometimes preceding the act with tongue flicking. They can give birth twice per year and there may be a correlation between fungi availability and annual birth frequency.
Gestation lasts between 144 to 159 days. Unlike other Callitrichidae species who produce twins, Goeldi’s monkeys only have one baby at a time. This is one of the reasons their genus (Callimico) is unique. These single births influence unique caregiving behavior and developmental outcomes compared to other members of the Callitrichidae family.
A single baby has its advantages; it allows for faster growth rates and earlier sexual maturity. Goeldi’s monkeys grow faster than other marmosets because they have a longer lactation period that provides vital nutrients. Additionally, for the first month of their lives, infants are constantly carried by their guardians. Clinging to the warm bodies of their parents allows youngsters to prolong using their energy for thermal regulation and activity, which is allocated towards their development.
After giving birth, a mother will act as the primary caregiver for the first 2–3 weeks until the father takes over. Non-parental group members will also assist in custodial duties. This communal care allows the mother to recover from gestation, birth, and lactation, although she will still nurse her offspring until they reach 65 days old. Some studies have reported some mothers transferred care as early as ten days, which is still considered late for other marmosets.
At 4 weeks, food is introduced to infants by group members, including mothers, fathers, and even other juveniles (usually older siblings). This provisioning also includes the robbing and removal of food to teach infants they will eventually have to forage on their own, which occurs at 7 weeks.
Over time, the diligent care and effort dedicated to raising an infant will wane. This transition to independence appears to be more forced than voluntary. Mothers become increasingly aggressive towards their young at 2–5 weeks of age. After 2 months, little ones will slowly begin to venture away from their carriers, and at 3 months old, their locomotion is fully autonomous. Young will engage in play for learning and exploration with other juveniles. Sexual maturity is reached between 18 and 24 months. In contrast, females in captivity become sexually mature at 8.5 months and males at 16.5 months
As fruit eaters, Goeldi’s monkeys are credited as seed dispersers, an important ecological role for biodiversity. The discarded or leftover seeds found in their droppings have the potential to promote new plant growth, diversify plant genetics, widen distribution, and provide vegetative restoration.
Within the food web, they act as a food source for their natural predators, including bush dogs, coatis, tayras (members of the weasel family), pumas, and snakes. Although some may think of it as sad, the predator/prey relationship is an important concept that helps maintain trophic balance and permits the transfer of food energy across ecosystems. However, it is speculated their sympatry with other primate species helps lower the chances of predation. There’s safety in numbers! It is also assumed they avoid birds of prey—such as hawks, eagles, falcons, and owls—by remaining low in the understory. Unlike many other Latin American primates, Goeldi’s monkeys descend to lower levels of the understory when threatened instead of fleeing to a higher level. These behaviors are thought of as tactical defense mechanisms that offer interesting insights for how they protect themselves and their families.
The International Union for Conservation of Nature lists Goeldi’s monkey as Vulnerable (IUCN, 2020), appearing on the IUCN Red List of Threatened Species.
It is suspected that a population decline of 30% or more over the course of 18 years will occur due to the threats faced by the species. The countries that Goeldi’s monkeys are found in are unfortunately listed as four of the world’s top seven countries in tropical forest decline. This can be attributed to climate change, human population expansion, the conversion of habitats to pastures, timber harvesting, slash-and-burn agriculture, and artisanal gold mining.
In 2017, a Peruvian wildlife trade evaluation uncovered that Goeldi’s monkeys were sold in a market for the second highest price of any other trafficked primate. They are hunted for food and the illegal pet trade.
The Goeldi’s monkey is listed in Appendix I of 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. Though this offers a level of protection, it still permits trade in exceptional circumstances.
National parks in Colombia (Amacayacu Natural National Park, Cahuinarí Natural National Park, and La Paya Natural National Park), Brazil (Serra do Divisor National Park), Peru (Manu National Park, Sierra del Divisor National Park, Los Amigos Conservation Concession, Pucacuro National Reserve), and Bolivia (Estaciones Biológicas de Abuná y Tahuamanu) provide a degree of protection for Goeldi’s monkeys; however, these protected areas make up less than half the forests in which they are found.
Several permanent research sites exists, such as Northern Illinois University’s Camp Callimico and Estacion Biologica Tahuamanu in Bolivia. Brazil is also home to the Florestal Estadual do Antimary and Peru has Centro de Investigación y Capacitación Rio Los Amigos (CICRA) and the Los Amigos Biological Station.
A modicum of optimism may be offered by the Goeldi’s Monkey Species Survival Plan®, a collaborative conservation effort throughout the Association of Zoos and Aquariums. Species Survival Plan (SSP) programs monitor wild and captive populations of endangered species. Cooperative breeding programs, research, public education, fundraising, field studies, and reintroduction are some of the conservation strategies.
Written by Dana Esp, December 2023