WESTERN PYGMY MARMOSET
Geographic Distribution and Habitat
The small but fierce western pygmy marmoset is a New World monkey and native to the western Amazon Basin. The western Amazon Basin covers the northwestern region of Brazil, southern Colombia, eastern Peru and Ecuador, and northern Bolivia. These arboreal (tree-dwelling) monkeys can usually be found where the vegetation is dense, near rivers or floodplains, jumping through the understory up to 66 ft (20 m) from ground level or clinging to tree trunks to feed on sap and gum. However, due to their small size, pygmy marmosets can be easy prey for eagles, hawks, wild cats, and snakes, so they prefer to stay in the understory of evergreen forests and avoid the top of the canopy and forest floor.
Size, Weight, and Lifespan
The pygmy marmoset is the New World’s smallest monkey, and one of the smallest monkeys in the world! Adults are 4.6 to 6.2 in (12 to 16 cm) long and weigh about 3 to 5 oz (85 to 140 g). Females are sometimes slightly heavier than males, but pygmy marmosets are not sexually dimorphic. These monkeys are so small, they can fit into a human hand and weigh as much as a deck of cards or a baseball. Their tails are longer than their bodies, measuring 6.8 to 9 in (17-23 cm), and are used to help these tiny creatures maintain their balance as they climb and jump between trees. However, unlike spider, woolly, and howler monkeys, their tail is not prehensile. It cannot grasp or hold objects. Pygmy marmosets can live to be 12 years old in the wild and up to 18 years in captivity.
A soft thick mane of golden brown fur, flecked with white and black, covers western pygmy marmosets’ heads. The mane stretches down around their large brown eyes and mouths and covers the ears. A small white stripe extends between their eyes and white brushstrokes of fur dot the corners of their mouths. Flexible necks can rotate their heads 180 degrees—useful when on the alert for predators.
Their underparts are colored tawny and orange. Black and brown “agouti” stripes provide camouflage against tree bark as they feed on tree sap in stillness. Their tails are ringed in black or brown.
Infants are born with grey heads and a yellow coat. They develop adult markings as they mature.
Pygmy marmosets have black, sharp claws—rather than flat nails like most primates—to help them climb and grip trees. In addition, and rather uniquely, their thumbs are not opposable like most other primate species are. Their back legs are longer than their front legs to help them leap up to 15 ft (4.5 m) in one thrust through the forest.
Pygmy marmosets are primarily gummivores; their diet consists mostly of tree exudates (tree sap, gum, latex, and resin) and some fruit, flowers, nectar, insects, and spiders. They have small, sharp bottom teeth that they use to gouge holes in trees and vines. Once the exudate starts to pool in the holes, they use their tongue to lick it from the tree. They start by gnawing holes in the bottom of the trees and work their way up the trunk until the tree no longer supplies an adequate amount of exudate. At this point, they move to a new tree and begin the process again. However, it is important to note that these primates do not kill the tree they are feeding from, but instead move from tree to tree to allow the tree to replenish itself.
In addition, the sap attracts insects and butterflies, and sometimes the monkeys wait for them to land before snatching them up for a meal. Pygmy marmosets can chew over 1,000 holes in one tree and they will often keep reopening a single hole so sap continues to run out of the tree or vine.
Behavior and Lifestyle
Families choose a sleeping site near their food source that is adequately covered to avoid predators. All group members wake up at sunrise. Typically, marmosets socially interact shortly after waking up and in the late afternoon before sleeping by grooming each other and playing. Between these times, their attention is focused on feeding and taking care of their young. Males are typically busier with taking care of the infants than the females, giving the females more freedom to forage.
Some tourists refer to pygmy marmosets as “little lions” because of their manes or “pocket monkeys” because they are so small.
Infant pygmy marmosets babble and make many baby noises until their vocalizations grow and change to resemble the calls and chatters of adults. This babbling stage is an important part of the infant’s development, and interestingly, their vocal development actually is very similar to a human baby’s.
Pygmy marmosets may be one of the world’s smallest monkeys, but they give birth to the largest primate infants when compared to the size of the mother. Infants are about .5 oz (14 g), which is about 14 percent of the size of an adult female. To put this into perspective, human babies are about 5 percent of the size of their mothers.
Pygmy marmosets are monogamous and find a mate to start their own family. Each group of pygmy marmosets usually consists of one couple and their young and extended family, called a troop. Troops typically vary from 2 to 6 members.
Although these monkeys are generally docile and friendly to family members, they are very territorial. Pygmy marmoset families have territories up to 100 ac (40.5 ha) marked by scent.
The adults in the troop work together to raise the young and watch for predators. When they are attacked, they work together to defend themselves by making loud vocalizations and counterattacking; however, they sometimes stay still until the predator leaves.
Pygmy marmosets communicate physically, vocally, and chemically to protect their families and mark their territories. They make facial expressions to show surprise, fear, and contentment through various movements using their lips, eyelids, and mane. In addition, male pygmy marmosets will arch their back and strut to show dominance or when they feel threatened.
They also create various vocalizations by making high-pitched trills and chatters to communicate. For example, when a pygmy marmoset makes a loud, open-mouth trill, this is to signal danger such as a predator, but a high-pitched, closed-mouth trill is used for recognition. To humans, these vocalizations can sound similar to bird calls. Some calls are so high-pitched that the human ear can’t hear them. Finally, pygmy marmosets use scent to mark their territory and to attract mates.
Each troop has one dominant female that produces offspring. When a female is ready to reproduce, she releases a chemical secretion from her genitals, chest, and anus to attract a mate. Once she finds a mate and becomes pregnant, her gestation period lasts for four and a half months. After the first mating, she can give birth about every five to seven months. Mothers almost always have fraternal twins. The babies weigh about 0.5 oz (14 g) and are about the size of a human thumb. After she reproduces the first time, she is ready to breed again three weeks after she gives birth.
The father takes on an active parenting role from the day of delivery, helping to deliver the infants, cleaning them, and taking care of them by carrying the newborns on his back for the first two weeks between nursings. Sometimes siblings help with the infants as well, hiding them while the other family members find food. At three months, the young pygmy marmosets are strong enough to keep up with the troop and are weaned from their mother. After one to one and a half years, young marmosets reach sexual maturity, and at two years of age, they are fully grown. At this point, they will typically stay in the troop for two more birth cycles to take care of new infants before leaving the group to begin mating and creating their own families. This group coordination allows the juveniles to learn parenting skills, and for the troop to continue functioning cohesively.
Pygmy marmosets act as seed dispersers by depositing seeds from the fruit they eat throughout the forest.
The International Union for Conservation of Nature (IUCN) categorizes the western pygmy marmoset as Vulnerable (IUCN, 2015).
The species is considered to be undergoing a population size reduction greater than 30% over a three generation period (starting in 2009) due to a continuing decline in area, extent and quality of habitat from deforestation, mining, oil palm cultivation, settlements and other anthropogenic threats, and from hunting.
Their habitat is impacted by the affects of human activities on the forests where the pygmy marmosets reside, including deforestation, mining, oil palm cultivation, settlements and other anthropogenic threats, and from hunting.
There is hunting in some parts of the range, for example, in Ecuador, as well as use as pets in Ecuador and Peru. Habitat loss is taking place in several areas of its range and local extinctions have been reported in areas in northeastern Ecuador.
Gallery forests along rivers, that are western pygmy marmoset habitat are preferred for human settlements and are severely affected by deforestation. Large areas of the distribution range of the subspecies are affected by mining, oil extraction and palm and coca plantations. Although western pygmy marmosets could use secondary forest if there are exudate sources, the disappearance of groups in this type of forests have been documented in the long term in several populations in Ecuador.
Researchers have observed behavioral changes in pygmy marmosets that are faced with interaction with humans, especially in areas with heavy tourism. Overall, pygmy marmosets within a habitat that is near human activity are less playful and less aggressive. As mentioned earlier, pygmy marmosets have a large set of complex and dynamic vocalizations for communication, but in areas with human interaction, these social primates become much less vocal. In addition, troops are forced higher into the rainforest’s understory and canopy than is the norm when they were undisturbed. In addition, the illegal exotic pet trade poses further threats to the viability of the species. Capture causes an even more drastic change in behavior and vocalizations. For these reasons, habitat protection is immensely important.
The western pygmy marmoset is listed on Appendix II of CITES (as Callithrix pygmaea).
There are many protected areas in Brazil, Bolivia, Colombia, Ecuador, and Peru where pygmy marmosets live. For example, in Bolivia, there is the Manuripi Health Nature Reserve, which protects pygmy marmosets from being hunted or captured and prevents their habitat from being destroyed. In Ecuador, Stella de la Torre and Pablo Yépez developed classes to educate children who live near pygmy marmosets’ habitat about the importance of protecting and respecting these tiny primates.
Written by Laura Fern, October 2017, Conservation status updated December 2020.