Geographic Distribution and Habitat
Sometimes referred to as Goeldi’s marmoset, Goeldi’s tamarin, or simply callimico (the species’ genus), this rare and petite New World monkey resides in the upper Amazon rainforests of southern Colombia, eastern Peru, western Brazil, and northern Bolivia. Groups are often separated by several kilometers, their locations determined by suitable habitat and availability of food, particularly the fungi that provide them with key nourishment.
These monkeys tend to spend most of their time in the dense, vegetative forest understory of primary forests, especially during the wet season (January and February). But they also inhabit secondary forests, patches of bamboo forest, treefalls (gaps in the forest where trees or large tree limbs have fallen), swampy and scrub areas, and stream edge forests, favoring these habitats in the dry season (May through July).
Due to their small and fragmented populations, few field surveys have been conducted on Goeldi’s monkeys.
Size, Weight, and Lifespan
Goeldi’s monkeys are small! They are only slightly larger than a squirrel, with a head-and-body length that ranges from 7.5 to 9 in (19 to 23 cm). Their non-prehensile tails are a bit longer than their bodies, ranging from 10 to 13 in (25.5 to 32.4 cm). They can weigh less than a pound, ranging from 12.5 ounces (350 gm) to 1.2 lbs (550 gm). Females tend to be a bit taller than their male counterparts but weigh a little less.
Captive Goeldi’s monkeys weigh 1 to 1.3 lbs (454 gm to 590 gm), slightly more than their wild and free peers.
Unique among marmosets, Goeldi’s monkeys have three molars rather than two. This is one of the reasons they are categorized as a unique genus, Callimico.
In captivity, the lifespan of Goeldi’s monkeys is about ten years; however, some have been documented as living into their early twenties.
Having only one sexual partner.
Incapable of grasping or gripping.
Having more than one mate.
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The soft, thick, and silky fur coats of Goeldi’s monkeys are most often various shades of black, but their pelage (fur coat) can range from blackish or dark brown, dark reddish or silvery brown, to jet black. Adults have a lustrous mane that drapes from their neck over their shoulders. Some Goeldi’s monkeys have red or silver highlights in their “poofy hairdo” on the crown of their heads; others have random white streaks surrounding their face or on their torso, and still others have lighter colored rings at the base of their tails. The skin on their expressive faces is dark and bare of fur.
Goeldi’s monkeys have toes that are fitted with claws instead of nails—except for their second toe, known as the toilet claw, which has a nail that the monkeys use for grooming.
Fruits, insects, spiders, scorpions, bird eggs, and even small vertebrates that include frogs, toads, and lizards comprise the meal plan of Goeldi’s monkeys. But their true pleasurable feast, and a critical dietary sustenance to the species, is fungi: specifically, jelly fungus (found at treefalls) and bamboo fungus. The monkeys consume the most fungi—more than half their diet— during the dry season, when it is plentiful. Fruits are eaten less during the dry season; however, they provide important nourishment and can comprise more than half the monkeys’ diet during the wet season.
Behavior and Lifestyle
An arboreal species (meaning they spend most of their time in trees), Goeldi’s monkeys move from tree to tree quadrupedally; that is, on all four feet with a gait that is reminiscent of a gallop. Excellent leapers and climbers, Goeldi’s monkeys use their hind limbs to generate momentum and are capable of leaping, in a vertical position, from one cluster of branches to another separated by distances of 20 to 26 ft (6 to 8 m)—an astounding acrobatic feat for a tiny monkey.
Although they spend most of their time foraging in the forest understory less than 33 ft (10 m) from the ground, Goeldi’s monkeys will climb to higher elevations to procure a delectable fruit. Occasionally they will forage on the leafy forest floor, either descending from tree trunks in a head-first or backward direction.
Most active during the daytime (making them a “diurnal” species), Goeldi’s monkeys spend their days traveling, foraging, eating, and resting. They tend to rest in smaller groups of one to four individuals. Social grooming is a common pastime while resting. At night, they sleep in trees that are 32 to 49 ft (10 to 15 m) in height; groups often sleep together in the hollows of trees or in dense thickets of vegetation.
Goeldi’s monkey takes its name from the Swiss naturalist Emil August Goeldi, who is credited with discovering the tiny primate.
It is the only species classified in the genus Callimico, first described in 1904.
In a behavior known in biology as “sympatry” (the term refers to when two different species or populations exist in the same geographic area and regularly encounter one another), Goeldi’s monkeys have been known to travel and forage with saddleback tamarins and moustached tamarins, following at the rear of these mixed-species troops. During rest breaks and overnight, however, the monkeys separate into their own species’ group.
A conjectured rationale for this sympatric relationship is that it increases the productivity of fruit foraging. Perhaps more importantly, this relationship allows the diminutive Goeldi’s monkey to travel more safely in higher levels of the forest.
The “safety in numbers” adage holds true when the species is threatened by potential predators, who include bush dogs, pumas, snakes, eagles, and hawks. Goeldi’s monkeys’ tendency to remain in the forest understory lessens their risk of being attacked by avian predators and allows them to hide from other predators in the dense vegetation.
Communication among Goeldi’s monkeys includes a wide range of vocalizations. Young infants use a whistle-like call to get the attention of their mothers. Adult Goeldi’s monkeys possess a repertoire of 50 calls that are categorized into different groups, including long-distance location, long-distance contact, short-distance contact, alarm, warning, short-distance location, and aggression. The sounds associated with these calls resonate in quiet whistles, chirps, screams, twitters, song, shrill notes, and an assortment of other high-pitched sounds that indicate a feeling, behavior, or specific announcement.
The monkeys also use olfactory (scent) communication to identify their territory, convey an invitation to mate, or to solicit grooming. Related behavior includes urine marking, scent licking, and rubbing various parts of their bodies to stimulate scent glands. Tail marking occurs when the monkeys urinate on their tail and then rub it on the scent glands of their genital area, torso, and chest.
Posturing behaviors include stares (to communicate a threat by the sender), yawns (frequent during rest periods), grimaces (to communicate appeasement on the part of the sender to hopefully halt an attack from an aggressor), tongue flicks (to communicate an intense threat), and open mouth with teeth exposed (occurring only in extremely hostile situations). When facing a threat, Goeldi’s monkeys assume an arched posture with the hairs of their body standing on end (piloerection), making them appear larger than their actual size. (In captive Goeldi’s monkeys, piloerection is an indicator of stress.) Other postures relate to mating and grooming.
Goeldi’s monkeys live in monogamous pairs or in multi-male/multi-female groups of up to ten individuals that include offspring. (Some studies suggest, however, that monogamy may be more exclusive to captive Goeldi’s monkeys and that wild Goeldi’s monkeys can be polygamous.) Mating occurs during the wet season. It is the female who solicits the male for copulation, and a group can include more than one breeding female. Females go into estrus several times a year (“polyoestrous” is the biological term) and have been known to give birth twice in one year. They give birth to a single infant after a 145 to 152-day gestation period. This is unique among marmosets, who typically birth twins, and another reason that Goeldi’s monkeys have been given a unique genus, Callimico. A mere ten days after birth, females can again go into heat (“post-partum oestrus” is the biological term).
For the first 10 to 20 days of their infants’ lives, mothers are the primary caregivers. Afterward, they transfer care of their infants to the fathers. Mothers continue to nurse their babies, however, and infants are considered weaned after about 65 days. Studies have shown that mothers become aggressive to infants between the ages of 2 to 5 weeks, so transferring child care to the dads is probably a good thing. Female offspring tend to be transferred to their fathers earlier than male offspring.
Play is an important behavior in infants and young, serving as an exploratory and learning function. Adult Goeldi’s monkeys, however, rarely engage in playful pastime.
After seven weeks, juvenile monkeys are capable of foraging on their own. Goeldi’s monkeys reach sexual maturity between 18 and 24 months, with females becoming sexually mature earlier than males. In captivity, the average age for sexual maturity in captivity is 57 weeks for females and 15 to 16 months for males.
Goedli’s monkeys act as seed dispersers by depositing seeds from the fruit they eat throughout the forest.
Goeldi’s monkeys are classified as Vulnerable by the International Union of Conservation of Nature (IUCN), appearing on the IUCN Red List of Threatened Species (IUCN, 2020). Although the species is not threatened with imminent extinction, populations of Goeldi’s monkeys are at risk of habitat loss due to logging and clear-cutting forests for agricultural use.
Unfortunately, because Goeldi’s monkeys are rare, their value on the international black market for the illegal pet trade is increasing. They are also hunted by local people for food.
In theory, Goeldi’s monkeys are afforded certain protections by 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. The species is listed in CITES Appendix I, which permits trade only in exceptional circumstances.
Those monkeys who live within the boundaries of national parks of Brazil, Colombia, and Peru are protected. However, little protection exists for these tiny primates across their range.
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 Kathleen Downey, June 2016