Golden-White Tassel-Ear Marmoset, Mico chrysoleucos
GOLDEN-WHITE TASSEL-EAR MARMOSET
Mico chrysoleucos
Geographic Distribution and Habitat
The golden-white tassel-ear marmoset (Mico chrysoleucos), more simply known as the gold-and-white marmoset and sometimes referred to as silky marmoset, is a tiny monkey native to Brazil, residing in the eastern region of the state of Amazonas within the Amazon rainforest in an area known as “the arc of deforestation.” Geographic distribution for this species is delimited by the Madeira and Amazon Rivers to the north, by the Aripuanã River to the west, by the Paraná do Urariá and Acarí Rivers to the east, and by the Maracanã River to the south. This updated range for the species reflects the findings of researchers who conducted ten field expeditions within the arc of deforestation to study Amazonian marmosets between 2015-2018.
Habitat is provided by secondary, lowland forests and also by two types of seasonal floodplain forests, known as várzea and igapó, within the Amazon biome. (The Portuguese word várzea translates to “meadow,” while the Portuguese word igapó translates to “root forest.”) Várzea forests are flooded by whitewater rivers, whereas igapó forests are flooded by blackwater (also known as freshwater) rivers. The intrepid researchers who conducted the ten field expeditions discovered that some populations of golden-white tassel ear marmosets live in permanently flooded forests.
Marmosets are divided into four genera: Callithrix, Cebuella, Callibella, and Mico. Prior to their reclassification under the genus Mico in the early 2000s, all Brazilian marmosets—including the golden-white tassel-ear marmoset—were classified under the genus Callithrix. Geographic distribution informed wildlife biologists’ decision to separate these marmoset species. Those marmosets occurring in eastern Brazil, predominantly within the Atlantic Forest, retained the genus Callithrix, while those occurring within Brazil’s Amazon Rainforest became classified as Mico.
In his 1977 treatise, the late American mammalogist Philip Hershkovitz argued that the golden-white tassel-ear marmoset should be regarded as a subspecies of the black and white tassel-ear marmoset, also known as the Santarem marmoset (Mico humeralifer). (At the time of Hershkovitz’s argument, the Santarem marmoset was still classified under the genus Callithrix, so C. humeralifer). While Hershkovitz’s work was lauded as a “monumental revisionary monograph,” his argument ultimately did not hold traction.
To date, the few taxonomic and phylogenetic (evolutionary) studies of Amazonian marmosets have been based, sometimes solely, on the morphology (structure of organisms) of museum specimens—and not on those wild, living primates in their natural habitat. Thus, the taxonomic classification for the golden-white tassel-ear marmoset (and its many “marmoset cousins”) is subject to change, dependent on future wildlife studies. More field expeditions like those conducted by researchers from 2015-2018 are necessary to better know this species.
Size, Weight, and Lifespan
Female and male golden-white tassel-ear marmosets are monomorphic, which is a super science-y way of saying that, apart from their respective genitalia, these tiny primates exhibit little differences in appearance. “Tiny” is an apt descriptor. The monkeys weigh a mere 9.9 to 10.9 ounces (0.28 to 0.31 kilogram) and measure just 7.5 to 10.2 inches (19 to 26 centimeters) in length. A nonprehensile tail adds another 12.6 to 15.7 inches (32 to 40 centimeters) to their slender frame.
Lifespan has not been reported, but it is known to vary among different marmoset species, with an average of 5-7 years. The Emilia’s marmoset (Mico emiliae), the golden-white tassel ear marmoset’s Amazon Basin cousin, may have the greatest longevity with a maximum lifespan of 18 years in the wild.
Appearance
Have you ever seen such a cutie patootie? Mother Nature certainly has packed an abundance of pulchritude into this petite primate. She powdered both the face and ears pink—attaching wild white tufts (tassels!) of fur to each ear (they look more like furred propellers)—and set gold-colored eyes above an unpretentious, flat and wide muzzle with sideways-pointing nostrils. Then she turned her attention to the marmoset’s pelage. A silky, white fur coat with subtle, yellow-golden undertones cloaks the tiny frame. Abdomen, forelimbs, and hind limbs are a deeper shade of gold as is the long tail, which is distinguished by faint bands from base to tip. No furry crown on this monkey’s head, as often seen in some other small monkey species—but when you are this adorable, you don’t need a crown. And, of course, there are those ridiculously alluring, untamed tassels that add to the golden-white tassel-ear marmoset’s beauty.
Like all marmoset species and their tamarin cousins, down-turning claws, rather than nails (as seen in most primates), are fitted to each digit—except for the big toe. Thumbs and big toes are not opposable. Their forelimbs are shorter than their hind limbs, resembling those of squirrels. If you were able to peek inside their mouth (maybe you have harbored a wish to be a dentist), you’d notice two molar teeth in either side of each jaw, rather than three, further distinguishing marmosets (and tamarins) from other monkeys. Procumbent (or protruding) incisor teeth at the front of the upper and lower jaw are the same length as the canine teeth (or fangs), enabling marmosets to gnaw holes into tree bark to get at gums and exudates—important components of their diet.
Diet
Golden-white tassel-ear marmosets are omnivores—meaning that they eat foods of both plant and animal origin. Fruits, flowers, nectar, tree gums and other exudates, bird eggs, and small animal prey (including lizards, frogs, snails, spiders, and insects) are on their menu. This diverse diet allows these tiny monkeys to obtain the nutrients necessary for them to thrive.
As you might expect, the Amazon rainforest offers a bounty of exotic fruits. A favorite comes from the guaraná plant (Paullinia cupana), which grows on climbing liana vines. Colloquially referred to as the “edible eyes of the Amazon,” the small red fruits with black seeds surrounded by white fruit pulp indeed resemble a human eye. A local myth attributed to an indigenous tribe says that guaraná’s domestication originated with the sacrificial killing of a young village child by an evil deity. A more benevolent deity then plucked the left eye from the child and planted it in the forest, resulting in the wide variety of guarana that is still present today. Local myth aside, our human medical community has embraced guaraná fruit as a potential “superfood.” Containing high levels of caffeine—as much as four times that of coffee beans—along with other psychoactive stimulants, guaraná is associated with improved cognitive performance and reduced physical fatigue. Researchers are currently studying its role in preventing cardiovascular disease and cancer, in regulating digestive/intestinal health through its antibacterial properties, as an anti-inflammatory agent, as an antioxidant, as an antidepressant . . . and as an aphrodisiac. (Note: you won’t find an aphrodisiac connection in the Reproduction section below!)
Other fruits that golden-white tassel-ear marmosets enjoy include açaí berries, cashews, passion fruits, guava, buriti (Mauritia flexusosa), jaboticaba (Plinia cauliflora) (also known as Brazilian grape tree), papaya, pears, and mangos.
Behavior and Lifestyle
Because limited wildlife studies have been conducted on golden-white tassel-ear marmosets, uncertainties remain—not only on taxonomy, phylogenetic relationships, and geographic distribution, but also on behavior and ecology.
Golden-white tassel ear marmosets are primarily arboreal primates, spending most of their time living in trees. Those who do not live in permanently flooded forests may occasionally descend to the ground to feed, or travel to and climb another tree. Their claws aid in climbing, allow them to cling to tree trunks, and assist in their quadrupedal locomotion (they use all four limbs to travel across branches). They might also leap from tree to tree, at impressive distances, considering their small size, using their tails for balance. Marmosets’ quick, somewhat jerky, movements have been described as squirrel-like. Their claws (like their incisor teeth) enable them to gouge tree trunks to stimulate the flow of gums and other exudates. As diurnal primates, these tiny monkeys are active during daylight hours, usually beginning activity as a group within an hour of sunrise.
Foraging and eating may be the most important activities during the course of a day (interspersed by rest breaks and grooming sessions), but playtime is also imperative—particularly for youngsters.
Overnight, these little monkeys sleep within tree hollows or dense vegetation. They curl up against one another for warmth (counterbalancing their body’s inability to maintain a core temperature; fortunately, their tropical environment never truly becomes cold) and also for protection.
It should come as no surprise that golden-white tassel ear marmosets are hyper-vigilant against potential predator threats, constantly scanning their environment. Predators include birds of prey, especially hawks and harpy eagles; snakes, and wild cats.
The word “marmoset” is derived from the French word marmouset, which loosely translated, means “shrimp” or “dwarf.”
Marmosets are known locally as zaris or sagoin.
Golden-white tassel-ear marmosets are highly social primates. While the size of a family group (known as a troop) can be as small as four members (or less), oftentimes a number of extended family members—as many as 8 to 20 individuals, compose a troop. Troop size depends on the availability of food sources within the species’ home range, which can be from 25 to 99 acres (10 to 40 hectares).
A strong social hierarchy defines a troop, with members deferring to the troop’s highest-ranking male and female, who are the alpha breeding couple. Just beneath this alpha breeding couple are their adult relatives (often siblings); beneath these individuals are the remaining troop members whose hierarchal status is based on age, with older members having a higher social ranking.
Individuals belonging to other marmoset species are known to leave their natal (birth) group upon reaching adulthood. Usually, when a primate leaves his or her natal group, it’s for mating purposes (particularly for males). This behavior has not (yet) been recorded for golden-white tassel ear marmosets. Researchers have noted, however, that when the breeding (alpha) male of a marmoset’s family group dies, the group may meld with another marmoset group.
Other marmosets who share the golden-white tassel ear marmoset’s geographic range within certain areas of the arc of deforestation include the Rio Acarí marmoset (M. acariensis) and the black-tailed marmoset (M. melanurus), allowing for the possibility of hybridization between the three species.
As one of the world’s most biodiverse places, Brazil’s Amazon Rainforest is home to a vast array of wildlife, including: jaguars (a top predator), sloths, black spider monkeys, giant anteaters, armadillos, tapirs, marsh deer, poison dart frogs, green anacondas, giant river otters, over 1,300 species of birds, and more than 378 reptile species.
Vocalizations are important in the daily lives of marmosets. They communicate with one another to share information about food sources, to keep track of group members while out foraging in dense vegetation, to alert one another to the presence of potential predators or invasive tamarin troops, or simply to convey their mood. Their wide repertoire of calls is gleaned largely from the heavily studied common marmoset (Callithrix jacchus), also known as the white-tufted-ear marmoset. But researchers appear confident that other marmoset species have access to the same vocal catalog to send messages, but they do so with a twist. In essence, marmosets within a family group create their own (conspecific) language. They “vocally label” other members (or, simply put, assign names to individuals), having learned this behavior, or language, from family members.
As example, golden-white tassel-ear marmosets inflect the whistle-like phee contact call with a distinct, high-pitched modulation to communicate with specific individuals, who respond to the call. They may use similar, acoustic calls to vocally label other members. Scientists have characterized the behavior of vocal labeling (or naming) as an indicator of high-level cognition—previously thought to exist only in humans, elephants, dolphins, and some parrot species. Research suggests that marmoset communication may be a precursor at to how humans developed language skills.
Besides the phee call, other marmoset calls include whirrs/trills (another type of contact call), chirps (emitted in friendly encounters), twitters (inter-group territorial calls), seeps (warning/alarm calls), ek (an indicator of mild anxiety), tsiks (emitted during aggressive encounters between groups), and rapid fire tsik (a loud mobbing call directed at a predator), and squeals or screams (a distress call heard particularly in captive marmosets when handled by humans).
In addition to vocalizations, marmosets use their olfactory senses (sense of smell) to communicate. A specialized nasal cavity, known as the vomeronasal organ, processes chemical signals to convey important information about the location of food sources, identity, reproductive status, and to mark their territory. The chemical signals are those secretions released from a marmoset’s scent glands—found on the chest, anus, and genitals—when the marmoset rubs these bodily areas against a substrate.
Mutual grooming (allogrooming) is an important activity that not only helps to keep one another’s fur coats free of parasites but also helps establish social bonds with one another. And while playtime is associated with youngsters, the activity remains an essential social aspect of life for adults, too. Individuals might also hug or nuzzle against one another or lick one another’s face. Those wishing to show dominance over another might rub his chest.
Studies of captive marmosets have found that the monkeys are sensitive to visual social cues and use their facial expressions to convey emotional states.
Both marmosets and tamarins are considered to be the most primitive monkeys because of their anatomical and reproductive characteristics.
Although reproductive health studies for golden-white tassel-ear marmoset species are lacking, sexual maturity is likely between 12 and 18 months (akin to other marmoset species). A female initiates copulation by flicking her tongue at the male. Generally, marmosets are considered monogamous; that is, a male and a female are exclusive mating partners, which is believed to be the case with golden-white tassel-ear marmosets. But researchers have found instances of flexibility in the mating systems of some marmoset species (when a group includes multiple breeding males or females). As example, common marmosets (Callithrix jacchus) practice polyandry (one female mates with multiple males). Other species appear to practice polygynandry (both males and females mate with multiple partners).
Twins account for about 80 percent of all births and are “dizygotic,” which means they are non-identical. A normal gestation period is between 130-170 days. Sadly, females experience a high rate of miscarriage due to their small size and their vulnerability to various stressors in their environment. They offset this loss by typically giving birth twice a year.
Infant care is a family affair. Marmosets represent just 20 percent of primates (including tamarins) who engage in cooperative breeding, meaning that all able members of a family group help care for infants. Infants are usually carried on their father’s back and are returned to mom when it’s time to nurse. While she is nursing, a mother must increase her food intake by 50 to 100 percent to produce sufficient milk for her twin babies. A mother nurses her young for 8 to 10 weeks; infants are considered weaned by the age of 3 months. At age 4-5 months, up to 10 months, they are considered juveniles. At age 11 months, they are considered subadults.
Like other frugivorous (fruit-eating) primates, golden-white tassel ear marmosets help to regenerate their forest habitat by dispersing seeds, via their feces, as they travel throughout their environment. They might also help with the spatial distribution (planting) of new tree growth, thanks to their bark-gouging behavior. Scientists have posited that by consistently choosing the same older trees to seek (gouge) exudates, they hasten the trees’ natural demise—thereby opening up the forest canopy, allowing in sunshine, to promote new tree growth.
Golden-white tassel-ear marmosets are classified as Least Concern (LC) by the International Union for Conservation of Nature (IUCN, 2015), appearing on the IUCN Red List of Threatened Species. But the caveat should be that scant conservation studies have been conducted. While no known significant threats put the species at risk of imminent extinction and the marmosets show some tolerance to environmental disturbances, they face perils from anthropogenic (negative, human-caused) activities. Habitat destruction is the primary threat, particularly development occurring alongside the Trans-Amazonian Highway. New roadways, the creation of hydroelectric power stations, and the expansion of cattle ranching further threaten the species’ habitat. All these anthropogenic activities have led to what is known as the “arc of deforestation.” This infamous region refers to a crescent-shaped belt of rapidly disappearing forest in the Amazon region, home to golden-white tassel-ear marmosets and their many cousins.
Other potential threats concerning conservationists include environmental crime: illegal land grabs, whereby “bad actors” seize land through criminal means, and illegal logging.
Golden-white tassel-ear marmosets 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.
The species occurs in several protected areas and indigenous territories, under the purview of Brazil’s Protected Areas and Indigenous Land edict. Five sustainable use reserves (SDRs) are also home to the marmosets. Despite these safety nets, deforestation has crept into these habitats.
While conservation programs such as The Mountain Marmoset Conservation Program, founded to protect the Critically Endangered buffy headed marmoset (Callithrix flaviceps) and the Endangered buffy tufted-ear marmoset (Callithrix aurita), no conservation program specific to golden-white tassel-ear marmoset has yet to be launched. Its classification of Least Concern should serve as impetus to protect the species before its survival becomes as dire as its buffy headed and buffy tufted marmoset relatives.
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Written by Kathleen Downey, November 2024