Common Marmoset, Callithrix jacchus
COMMON MARMOSET
Callithrix jacchus
Geographic Distribution and Habitat
Common marmosets (Callithrix jacchus), also known as white-tufted ear marmosets, are native to the northeastern region of Brazil. Due to the ongoing destruction of their original habitat in the Atlantic coastal forest, common marmosets live in a range of climates and ecosystems, spreading inland through the dry Caatinga scrub forest to the Cerrado savanna in central Brazil.
While the Atlantic coastal forest is one of the world’s most biodiverse areas, the dry forests in central Brazil are a harsher environment, with less species diversity, shorter canopies, and greater seasonal variability in temperature and rainfall. However, common marmosets are highly adaptable and are able to thrive on the edges of these hostile forests, and have even made homes within cities such as Rio de Janeiro and Buenos Aires.
Size, Weight, and Lifespan
The marmoset family are the world’s smallest primates. A common marmoset measures from 6-10 inches (15-25cm) long, not including their long tails. Males are slightly larger, averaging about 7.4 inches (19 cm) long, and females averaging 7.28 inches (18.5cm) long. Their tails more than double their length, ranging from 10 to 16 inches (25-40) long! Common marmosets weigh less than a pound when they are full-grown. The average male common marmoset weighs 9.03 ounces (256 grams), and the average female weighs 8.32 ounces (236 grams). Common marmosets live about 12 years in the wild.
Appearance
Common marmosets have pale skin on their face surrounded by dark fur. They have round, curious eyes. The thick fur covering their bodies is mottled brown, black, and yellow. Different individuals have varying shades and color patterns. They have white stripes down their backs and long tails. Most notably, they have white tufts of fur that stick straight out from their temples, hiding their small ears, and giving them their nickname.
Diet
Common marmosets eat both plants and small animals. They are known as exudivore-insectivores. The primary source of food for the common marmoset is plant exudates, meaning the gum, sap, latex, or resin that ooze from plants. Common marmosets have short canine teeth and long lower incisors, which enable them to gnaw on bark as they cling to trees with their claw-like nails. They lick or scoop the exudates into their mouth. Since they are so small, they can get all necessary protein from insects. However, they also eat a variety of plants including fruits, seeds, flowers, fungi, and small animals such as lizards, tree frogs, and other infant mammals.
Behavior and Lifestyle
Common marmosets are arboreal, meaning they live in trees, and diurnal, meaning they are active during the day. They sleep in trees covered in vines and other vegetation. Although they leave their sleeping site for almost the entirety of daylight hours, they spend over 50% of their day relaxing and may remain unmoving for up to 30 minutes at a time. Common marmosets spend most of their active time foraging for plant exudates. In addition to creating their own gouges in plants, common marmosets also seek holes left by other animals or natural tree injury to collect exudates. They live in areas where there is high density of gum trees, which allows them to keep their home range small, about .002 to .03 square miles (.005 to .065 square kilometers). They navigate their environment by running quadrupedally (on all fours) across branches and leaping across trees. They use their claw-like nails to hang vertically on trees.
Natural predators of the common marmoset include arboreal snakes, owls, and wild cats. The marmosets sleep together, which functions as protection from predators along with the vegetation covering their sleeping site. Common marmosets also have a communication system that includes alarm calls to warn when predators are near.
Common marmosets can produce offspring that are genetically the offspring of their nonidentical twin, instead of their own. This is called germline chimerism.
The development of the whites in their eyes is highly correlated with non-maternal infant care, which is a crucial part of the common marmoset family structure.
Common marmosets live in social groups that range in size from 3-15 individuals. The average size of a common marmoset group is 9. The group typically includes one breeding female, although there may be two, and a breeding male. Nonbreeding adult females in the group are closely related to the breeding female, including her mother, daughters, or sisters. Common marmosets do not breed with others they are closely related to, and so males immigrate from their mother’s group to seek a breeding female when they reach adulthood. Adult males are not related to the other adults in their group. The social hierarchy is connected to breeding status. The breeding pair is codominant. Age determines the hierarchy of the non-breeding adults after the breeding pair. If there are two breeding females, one will be dominant over the other.
The common marmoset’s social group is their community. They are a caring primate and work together to care for and protect each other. A common marmoset’s vigilance increases when in the presence of an infant. They are also more vigilant when in a pair, and while one in the pair is eating, the other will take on a “lookout,” role.
Common marmosets have a considerable communication system that includes a variety of acoustic and visual signaling. Like humans, common marmoset infants engage in babbling stages as they build intentional communication skills. They have specific sounds that communicate specific messages and use individual vocal patterns to identify each other at a distance. They take turns when engaging in conversation with one another.
There are three basic types of vocalizations made by common marmosets.
A phee call is used at long distances. These calls allow common marmosets to keep track of where others in their group are, and to reunite. These calls are loud and high-pitched in order to be heard at long range.
A trill call is exchanged typically when foraging or resting nearby, usually within sight of one another.
A food call communicates when high-value food is found, and is an invitation to share with the group. Food calls can be long-distance.
With both phee calls and food calls, there is an aspect of individuality that allows others within the group to identify who the call is coming from by voice/sound only. However, in a trill call, common marmosets lose some of the uniqueness of their own call and sound more similar to the individual they are speaking directly to.
When a predator is near, common marmosets plan for the protection of the group and communicate that plan with each other. Different vocalizations communicate different plans of protection such as hiding or coming together as a group to threaten the predator.
Common marmosets also use nonverbal communication. They communicate their emotional state through facial expressions. Common marmosets maintain social eye contact more similarly to the way humans do than other closely related primates. Unlike with other primates, eye contact between common marmosets is not perceived as a threat, but rather is a tool for coordination and maintaining safety, for example, when two adults pass an infant between each other, or gather food together. They can also track where others are looking to communicate where there may be food or a predator.
Common marmosets reach sexual (reproductive) maturity at about 15 months of age. Females flick their tongues to attract a mate. While most mating is monogamous, there may be instances of polygyny or polyandry. Once females begin to reproduce, they continue for the remainder of their adult lives. The gestation period (pregnancy) is about 5 months. Common marmosets typically have a set of non-identical twins, although they can have a single birth or triplets. They typically give birth twice a year, in the fall and spring. This aligns with the end of the dry season and the end of the rainy season, which allows for more abundant food sources when the group is caring for newborns.
Infants nurse until they are about three months old. However, once they are weaned, infants do not immediately gnaw their own holes in plants; they are provided exudates by the adults in the group. Common marmosets are considered juveniles when they reach five months, and typically another set of infants are born at this time. The onset of puberty typically begins between 9 and 14 months of age. While there may be two breeding females in a group, the presence of a breeding couple usually suppresses the sexual development of young. Often the pregnancies of the nondominant female are not viable until she leaves the group. It is unclear what conditions allow for a successful birth from the nondominant breeding female.
The common marmoset family displays the ideal of “it takes a village,” to raise young. Infants may be 20 to 27% of their mother’s weight, which means pregnancy and nursing are very taxing on the mother. All members of the group contribute to the care of the infants. Fathers and extended family immediately begin supporting with carrying infants on their backs after birth. When infants are two weeks old they begin building locomotive skills and exploring their surroundings by crawling on their carrier’s back. Juveniles play with infants, which is beneficial to the physical and social growth of both the infants and the juveniles.
There is a gaping hole in scientific research regarding the common marmosets’ ecological role in nature. Due to the similarities between the common marmosets’ biology and social behavior, and that of humans, most to all accessible peer review research revolves around biomedical research on this precious primate, which is, in fact, a major threat to their survival. What we do know about their social and cognitive intelligence, and their evolutionary adaptability should spark curiosity to understand the ways in which the common marmoset contributes to their environment.
The International Union for Conservation of Nature lists the common marmoset as Least Concern (IUCN, 2015), appearing on the IUCN Red List of Threatened Species. While the common marmoset population is declining, it is not declining at a “fast enough” rate to warrant a more severe rating. It is important to note that common marmosets are not categorized at a higher threat level because of their resilience and adaptability. Common marmosets face significant threats, mostly from humans. They continue to face habitat destruction, they are frequently used in biological studies, and they are victims of hunting and capturing, primarily for the illegal pet trade.
The common marmoset is 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.
While there are specific conservation efforts for the common marmoset’s habitats, like the Atlantic Coastal Forest, there is little evidence of efforts specific to this monkey. Unfortunately, the common marmosets’ resilience has left them to continue to fight for themselves, despite much of the threat originating from human behavior.
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Written by Brandi Bellacicco, May 2024