High above the Amazon rainforest floor, in the soaring tropical canopy, lives the world’s smallest monkey, the pygmy marmoset (Cebuella pygmaea), also known as the pocket monkey, or dwarf monkey. While the pygmy marmoset is the world’s smallest monkey, it is not the world’s smallest primate: that distinction belongs to the mouse lemur, which like all lemurs is endemic to the forests of Madagascar.
A fully grown marmoset would fit easily into the palm of a human hand. These orange-brown primates, with their thick fur that makes them seem a little larger than they actually are, weigh between 3 to 5 ounces (85 to 140 grams) as adults, and at birth can weigh as little as 0.40 ounces (11 grams). Mature by the age of eighteen months or two years, in the wild pygmy marmosets are thought to live for an average of twelve years, while in captivity they have been known to live for up to eighteen years.
These miniature monkeys’ tails are longer than their bodies, and although they are not prehensile, they help the animal to maintain its balance as it moves through the rainforest canopy. While most primates have opposable thumbs and flat nails, the pygmy marmoset’s nails are claw-like, serving as an aid to climbing tree trunks, and it does not possess opposable thumbs.
Pygmy marmosets inhabit the Amazon rainforests of Brazil, Colombia, Ecuador, Bolivia and Peru, and they can be seen in the forest canopy within Tambopata National Reserve. They tend to form a group of no more than nine individuals, which will establish itself in a small territory usually no larger than about half an acre. Within this small group, pygmy marmosets are highly social, spending much of their time contributing to cooperative care groups and predator vigilance, when not foraging for food. Males care for the young, carrying them on their backs, while females take on extra foraging duties.
As part of their complex social system, pygmy marmosets employ a range of vocalizations, from the infant babbling of the young to the contact calls used my adults as they forage across their range.
In addition to its size, what marks out pygmy marmosets from other species of New World monkey –including the other seven monkey species found in Tambopata National Reserve- is their highly specialized diet, consisting of tree sap. Employing an up-and-down sawing motion, they use their specially adapted sharp lower teeth to cut a hole in the trunks or branches of woody plants in order to stimulate sap production, allowing a puddle of sap to accumulate before lapping it up with their tongues. Although they will also feed on insects, fruit and nectar, carbohydrate-rich sap forms the cornerstone of their diet.
While not endangered, their fame as the world’s smallest monkey has led to pygmy marmosets being exploited by the international pet trade, with a rise in their popularity in recent years among China’s growing middle class fueling the trade in these fascinating animals.