Mico humeralifer

Geographic Distribution and Habitat

The black and white tassel-ear marmoset, also known as the Santarém marmoset or tassel-eared marmoset, is endemic to the secondary Amazonian lowland rainforest area at the junction of the states of Pará and Amazonas, in Brazil. This area is delimited by two rivers: Rio Maués in the West and Rio Tapajós in the East.

Black and white tassel ear marmoset geographic range. Map: IUCN 2008

Size, Weight, and Lifespan

There is no significant difference in the sizes of male and female black and white tassel-ear marmosets. They weigh 11 to 12 ounces (300–400 g) on average and measure 7 to 11 inches (20–27 cm). Their tail is longer than their body at 12 to 14 inches (31–37 cm).

Although there is no official known lifespan documented for the species, several sources indicate that they may live up to 7 years in the wild and up to, or over, 16 years in captivity.


Black and white tassel-ear marmosets are covered in long soft hair. The mantle and saddle are gray with speckles of white. The belly, neck area, and limbs are a light cream color. Their tufted ears are fluffy with hair growing on the inside and shooting outward—similar to tassels of silk threads. Their face, which is not very hairy, is pigmented with patches of black, except around the eyes and mouth, where the bare skin is pink. Their eyes are big, round, and forward-facing. Their nostrils look like two black dots a short distance above the mouth. These little creatures have two lower molar teeth on each side of the jaw (other monkeys have three), and their lower incisors are almost equal in size to their canines—which is helpful for gnawing on bark. All of their fingers, except the big toe, have claws rather than nails. Their non-prehensile tail, which is not able to grasp objects, is striped with black and gray fur. They are the only marmosets with a ringed tail.

Photo credit: ©Sidnei Dantas/iNaturalist/Creative Commons

Black and white tassel-ear marmosets are mostly frugivorous (fruit-eaters), but they also eat seeds, flowers, nectar, birds eggs, and, if opportunity arises, small prey such as arthropods, small lizards, or frogs. They manipulate food with their hands, while standing on branches. Their sharp claws allow them to cling vertically while poking holes in tree trunks to extract sap. In fact, they heavily rely on exudates (sap, latex, resin, and gums) for subsistence when fruit is less abundant. They are able to process fruits because their digestive tract has a large caecum, the pouch that is considered to be the beginning of the large intestine. Once digested, these food items provide the marmosets with carbohydrates, proteins, and minerals (mostly calcium).

Behavior and Lifestyle

These social primates live in groups of 5 to 15 individuals, with typically one dominant breeding female and one or more breeding male. They live at altitudes below 650 feet (200 m), and they spend most of their time in the canopy.

Black and white tassel-ear marmosets live in close proximity to and share resources with other monkey species, including howlers, capuchins, and squirrel monkeys.

Daily Life and Group Dynamics 

These little creatures are very active. They leap from branch to branch, walk and run on four legs, hang upside down, or cling to tree trunks. Members of a group stay in close physical contact with one another. Their days are spent foraging, playing, and resting. While playing, they chase and mount each other, pounce, wrestle, roll, tumble, and vocalize. Play sessions help young marmosets learn the skills they need to socialize, but also to hunt small prey (pouncing) and defend their territory (chasing). Fortunately, the bouts of tense energy that occur when encountering neighboring groups of marmosets rarely end in fights. All these moments of excitement are usually followed by grooming sessions. One individual may groom another or several individuals may congregate and groom together. Grooming allows them to bond and relax.

At night, small groups of marmosets curl up in tree holes, where they are hidden and safe from predators while sleeping.


Communication is part of the social life of marmosets. They use different vocalizations and physical behaviors to express different things in different contexts.

“Trills” are used by group members to keep in touch. High-pitch long calls—also referred to as “phee” calls—are used for long distance communication to find lost members of the group, attract a mate, or dissuade outsiders from getting too close. These calls encapsulate important information about the “speakers”—their gender, identify, group affiliation, and location.

A recent study revealed that “phee” calls are equivalent to words or sentences in human conversations. The marmosets engaged in a dialogue don’t need to be related and each patiently waits for the other marmoset to finish their call before responding. There is no interruption or overlap. Although the study focused on the common marmoset, we may assume that the same is true for the Santarém marmoset.

Alarm calls are short high-pitch staccato calls used in presence of danger. Marmosets may use these calls alone or in addition to scent-marking trees at the edge of their territory with their chest and anal glands. They may also call while staring at an opponent with a partially opened mouth. Cuff sounds, arched walks, and piloerection (bristling of hairs due to the involuntary contraction of small muscles at the base of hair follicles)  are other ways marmosets display to discourage intruders.

In captivity, black and white tassel-ear marmosets were observed vibrating their tongue and producing cricket sounds—which were louder with the mouth open than with the mouth closed—the meaning of which has yet to be identified.

Reproduction and Family

Individuals of both genders become mature when they are one and a half years old, but males do not sire offspring until they are at least two. Sixty percent of marmosets disperse to other groups to breed by the time they are three years old; ninety percent disperse by the time they are four.

When in estrus, females display a slight swelling and may entertain relations with several males. After a gestation of approximately 5 months, the mother gives birth to a set of twins. In rare cases, more than two babies are born, but typically only two survive—maybe because females only have one pair of nipples.

Although there are no specific data available pertaining to this species, in other marmoset species only the dominant female breeds, even if a group includes several adult females. We may assume this to be true for the black and white tassel-ear marmoset as well. Should a low ranking female give birth, she would have to isolate with her infants for 10 days after to prevent infanticide by other females—a phenomenon observed in some marmosets.

Newborns weigh just about 1 ounce (28 g); they are 3 inches (7 cm) long and they do not yet have ear tufts. Babies start eating solid food a one month old, but continue to suckle and are weaned at six months of age.

Because raising twins is energetically taxing, alloparenting is common; adult males and other members of the group carry infants to alleviate the mother’s load. The young learn how to forage, behave, and even communicate from other members of the group. They gain the ability to produce calls as their nasal cavity, larynx, and lungs develop, and learn “language” from the vocal feedback they receive from the adults around them.

Photo credit: © Gabriel Leite/iNaturalist/Creative Common
Ecological Role

Black and white tassel-ear marmosets are good seed dispersers and contribute to the health of the forest.

Conservation Status and Threats

International Union for Conservation of Nature classifies the black and white tassel-ear marmoset as Near Threatened (IUCN, 2020), appearing on the IUCN’s Red List of Threatened Species. How many individuals are left in the wild is unknown.

As in many parts of the world, primate populations in South America are declining due to habitat loss. These monkeys are no exception, even if they are able to survive in second growth forest, selective logging forest, and low forest with lots of lianas. Urban expansion, slash-and-burn activities to convert forest for agriculture and cattle ranching, timber harvesting, road construction, and the development of energy infrastructure (especially hydro-electric plants) all contribute to deforestation. According to Global Forest Watch, the state of Amazonas has been subject to significant deforestation over the last fifteen years. If the trend continues, black and white tassel-ear marmosets could lose 10–15% more of their forest habitat by 2035.

Highways traversing the forest are causing these marmosets to be killed while attempting to cross from one area to another.

Because they are so cute, they are attractive candidates for the illegal pet trade.

Finally, climate change models show that temperatures in northern Brazil will increase by at least 3.6 degrees F (2 degrees C) and up to 12.6 degrees F (7 degrees C) by 2050. This will not only negatively impact the food and water resources these primates rely on for survival, it will increase the number of disease-carrying insects, thereby putting their health and that of humans at higher risk than today.

Conservation Efforts

Several conservation projects are in place to mitigate the ill-effects of deforestation and the loss of biodiversity—even if they are not specifically targeting conservation of black and white tassel-ear marmosets.

The Amazon Region Protected Areas (ARPA) divides the Amazon forest in fully protected areas and in sustainable development reserves. Harvesting natural resources for commercial gain is not allowed in fully protected areas. The goal is to increase the surface of protected forests in the Amazon from 37% to 46% by 2030. This project is managed by the Brazilian Ministry of Environment and implemented by the Brazilian Environmental Agency (IBAMA) with the support of the World Bank, the World Wildlife Fund, the Global Environmental Facility, and the German Aid Agency.

The Tapajós Basin Blueprint is a project that the Nature Conservancy is developing to help identify areas of priority for conservation, restoration, and economic activities along the Tapajós river.

The Micos Urbanos Project in Itaituba (PA) focuses on identifying places where marmosets (including the Santarém marmoset) live near urban areas to develop conservation action plans.

  • ​IUCN Red List –​
  • Mico humeralifer (Primates: Callitrichidae) – Guilherme S. T. Gambino; Fabio O. Nasicmento (Mammalian Species, Volume 46, 2014)
  • A global risk assessment of primates under climate and land use/cover scenarios (2019) – Joanna S. Carvalho, Bruce Graham, Christoph F. J. Meyer, Serge Wich 
  • Coupled Oscillator Dynamics of Vocal Turn-Taking in Monkeys – Daniel Y. Takahashi, Darshana Z. Narayanan, Asif A. Ghazanfar
  • Ecology and Society (march 2020) – Integrating Ecosystem Management, Protected Areas, and Mammal Conservation in the Brazilian Amazon – Claudia Azevedo-Ramos, Benedito Domingues do Amaral, Daniel C Nepstad, Britaldo Soares Filho and Robert Nasi
  • Callitrichines – The Role of Competition in Cooperatively Breeding Species – Leslie J. Digby, Stephen F. Ferrari, Wendy Salesman
  • – Nature Conservancy website – The Tapajos River – Hope for Sustainable Development
  • – marmoset care – Understanding marmoset behaviour
  • – Science Magazine – Marmoset baby talk
  • ​ website

Written by Sylvie Abrams, December 2020