Mico melanurus

Geographic Distribution and Habitat

First described in 1812, black-tailed marmosets (Mico melanurus) are native to the South American countries of Bolivia, Paraguay, and Brazil, east of the Rio Aripuana. They live in a wide array of biomes, including the deciduous forests of eastern Bolivia, the Pantanal wetlands, the dry forests of Paraguay, the Amazon rainforest, and the Cerrado savanna of Brazil.


Marmosets are split into four genera: CallithrixCebuellaCallibella, and Mico. Black-tailed marmosets were previously considered to be a subspecies of the silvery marmoset (Mico argentatus), until they were elevated to full species status in 1991. As a result, they are little-studied in their own right, but we can fill in the missing pieces based on the better-studied lifestyle of the silvery marmoset. Marmosets and their cousins, tamarins, are thought to be the most primitive monkeys.

Black-tailed marmoset geographic range, IUCN 2008

Size, Weight, and Lifespan

Black-tailed marmosets are small primates. Adult head and body length is 6–10 inches (18–22 cm), and they weigh about 10–14 oz (300–400 g). Relatively short-lived primates, marmosets typically live up to 12 years in the wild and 16 years in captivity.


The coat, or pelage, of black-tailed marmosets is a light brown color over their forelegs, chest, and neck, and a darker brown on their back, hind legs, and head. Their upper thighs are a distinct whitish-yellow color, and their ears and nose are bare, showing pink skin. As their name suggests, their tail is all black, and it is not prehensile, that is not able to grasp or hold objects. Like all marmosets, they have long, curved claws as opposed to nails on their feet and hands, which help them to climb trees. They have very strong teeth with thick enamel, necessary for gouging trees to access sap.

Photo credit: Mike Griffiths/Creative Commons

Black-tailed marmosets primarily consume exudates, such as sap, gum, and resin. They also eat fruits, flowers, nectar, seeds, and fungi, as well as invertebrates and small vertebrates.

Behavior and Lifestyle

Black-tailed marmosets are arboreal (tree-dwelling) and diurnal (active during daylight hours). A closely related species, the silvery marmoset, spends its nights sleeping in tree hollows and dense vegetation, and this is likely also true of the black-tailed marmoset. They use their long, curved claws to grip tree branches and trunks, moving quadrupedally (on all fours) through the trees. While they are not known to be particularly accomplished jumpers, black-tailed marmosets can make short leaps to travel from branch to branch. Marmosets typically defend home ranges of about 25–100 acres (10–40 ha).

Fun Facts

The birth of twins is rare in most primate species, and when they are born, it is rare that both infants survive to adulthood. Marmosets and tamarins, however, are the only primates besides humans to be consistently successful at rearing twins.​

Daily Life and Group Dynamics 

Like most primates, black-tailed marmosets are highly social. Their average group size is about six individuals and is usually composed of a mated pair and their offspring. Males disperse from natal groups upon reaching maturity. They are territorial, chasing away individuals invading their home range.

Marmosets regularly perform acts of altruism, sharing food and resources with groupmates. Surprisingly, marmosets perform these acts more frequently when other groupmates are not watching. One study found that when an adult and infant were alone together, the adult shared their food with the infant 85% of the time. When in a group, the adult shared their food 67% of the time. While altruism is not an extreme rarity in social species, this pattern is very unusual. Under commonly accepted models of altruism, one would expect these acts of kindness to occur more when they are witnessed by adult groupmates, showcasing the do-gooder’s material wealth and elevating his or her status in the group. One possible explanation for this odd pattern is that it is a marmoset version of the bystander effect: when in a group, the adult with food feels less personally responsible for providing food for the infant than when the adult and infant are alone together.


​Black-tailed marmosets are extremely communicative, relying on many different methods of communication. Vocal communication methods include: shrills, which are used as a contact call for groupmates; trills, which are used for adult-infant interactions; and chirping, which is used when food is found. Interestingly, marmosets tend not to interrupt each other when communicating vocally, instead allowing others to finish their vocalization before they begin. Olfactory methods include anal and sternal scent marking. Visual communication includes: rolling, which initiates play with another group member; head cocking, which is displayed when an individual sees an object of interest; and head tossing, which is used as an aggressive display in intergroup conflicts. Finally, tactile forms of communication include: cuffing, the striking of another individual sharply with the hand, which is used to chastise a younger group member; gentle biting, a way to initiate and engage in play; and body rubbing, which is an amicable display often seen between newly paired individuals.

Reproduction and Family

​A rarity in the primate world, marmosets usually birth twins, although triplets and single births are possible. Gestation time in a closely related species, the silvery marmoset, is 145 days, and their interbirth interval is 5.5–10 months. Subordinate female marmosets are prevented from ovulating by the pheromone secretions of dominant females, preventing lower-ranking females from reproducing. Marmosets are the embodiment of the phrase “it takes a village to raise a child” (or two, in their case). Infants are raised communally, with all members of the group playing a role in child-rearing. Paternal caregiving is particularly important, as primarily fathers carry infants and bring them to their mothers to be nursed every few hours. Infants are weaned at around six months and reach sexual maturity at about one year old.

​Ecological Role

Because the tree exudates on which the black-tailed marmosets feed are highly abundant, inter- and intraspecific competition for food is likely not an important factor for them. Interspecific means within a species. Intraspecific means between individuals of different species.

They play a predatory role on the small invertebrates and vertebrates that they eat, and they may play a role in seed dispersal by consuming fruit. Black-tailed marmosets’ small size and diurnal lifestyle makes them potential prey for a slew of predators, including snakes, cats, and raptors.

Conservation Status and Threats

Black-tailed marmosets are currently considered Near Threatened by the International Union for Conservation of Nature (IUCN, 2015), based on a projected loss of tropical forest habitat of between 15–20% that will likely impact their current (2019–2024) and two subsequent generations (2025–2030; 2031–2036). In combination with the fact that this species is sometimes taken for the pet trade, its conservation status very likely approaches the threshold for Vulnerable.

Principal threats include fires, rural colonization, agriculture, cattle-ranching, urban expansion, deforestation, power grids, road networks, degradation and fragmentation of its forests, and to a lesser extent capture for pets.

In Paraguay in particular, black-tailed marmosets are one of only five species of native primate, in contrast to neighboring Brazil’s 77 native species. Paraguay has seen rampant deforestation in recent years, losing almost 17,000 square miles (44,000 square km) of forest between 1987 and 2012. This is particularly worrisome because the distribution of black-tailed marmosets is not solidly understood. As recently as 2017, the species has been found in new areas. This means that the rampant land use changes affecting Paraguayan wildlife are occurring before we have a solid understanding of what exactly is being lost.

Unfortunately, marmosets are a common type of monkey to be kept as pets. While exact figures are not known, there is evidence that black-tailed marmosets are collected in the wild for the pet trade.

Conservation Efforts

As with many primate species, including many designated as Least Concern, there is a need for more basic research on the life history, ecology, population size, distribution, and population trends of the black-tailed marmoset, as well as information about threats facing the species. It is impossible to make sound management decisions without knowing this basic information about a species.

Black-tailed marmoset habitat is protected in part by numerous protected areas, including the Noel Kempff Mercado National Park in Bolivia, the Pantanal Matogrossense National Park in Brazil, and the Defensores del Chaco National Park in Paraguay. It is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES).

  • Burrows, A. and L. Nash. 2010. The Evolution of Exudativory in Primates. Springer Science & Business Media: New York.
  • Marques, A., M. Schneider, C. Alho. 2011. Translocation and radiotelemetry monitoring of black-tailed marmosets, Callithrix (Mico) melanura (É. Geoffroy in Humboldt), in a wildlife rescue operation in Brazil. Brazilian Journal of Biology 71(4).​
  • Noronha, M., W. Spironello, D. Ferreira. 2008. New Occurrence Records for Mico melanurusNeotropical Primates 15(1):28-28.
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Written by K. Clare Quinlan, May 2020