Distribution and Habitat
These marmosets are found in the Upper Amazon basin east of the Andes in Colombia, Ecuador, Peru, Northern Bolivia and Brazil. They have a patchy distribution in mature and secondary lowland rain forest, especially seasonally flooded forests, river margins, flood plains, and stream sides. They are rarely seen in the trees above 60 feet (18 m) or on the ground.
Pygmy marmosets are the world’s smallest true monkeys. (The smallest primate is the pygmy mouse lemur.) Pygmy marmosets are not sexually dimorphic. Adults are about five inches (13 cm) long with an eight-inch (20 cm) tail and weigh four to seven ounces (113 to 199 g). The fur is buff and gray with yellow and green striations, which give it a grizzled effect on the head and back and a vague banded effect on the tail. They have long hair on their heads and chests giving the appearance of a mane. Their coloration provides great camouflage for their lives in the trees.
They are active and agile creatures, running, jumping, and occasionally leaping among trees and shrubs. These little monkeys move quadrupedally through the trees in an upright position. Their forelimbs are shorter than their hind limbs and they often feed while clinging upright to a trunk or branch with their sharp claws. They have claws on all digits except the big toe, which has a flat nail.
Their cryptic coloration and small size, along with movements that include squirrel-like dashes, sloth-like oozing over tree trunks and abrupt and frozen stillness can make them quite difficult for predators to see.
Pygmy marmosets are arboreal and diurnal—they live in trees and are active during the day. They are also usually docile and gentle. Mutual grooming is often seen between members of a group as part of their social bonding. Pygmy marmosets are very territorial and mark and defend territories from 25 to 100 acres. They mark their territory with scent glands located on the chest and suprapubic area. Defense of territory involves calls, displays, and sometimes chasing away others.
They are found in groups of two to six. The group is made up of an adult pair and its offspring. The monogamy practiced by this species is notable because monogamy is fairly rare in both mammals and primates. Pygmy marmosets sleep in tree holes or vine tangles located near their current primary feeding source.
They communicate using scent markings and calling (high bird-like sounds). They also communicate with members of their groups through facial expressions and posture. In addition to the high-pitched whistles and twitters, pygmy marmosets also produce an ultrasonic cry expressing hostility that is inaudible to humans.
Basic calls include:
* Open mouth trill: loud, alarm
* Closed mouth trill: squeaky, contact
* Twitter: submissive
Reproduction and Development
Fraternal twins every five to six months are the reproductive norm of these marmosets (although one or three offspring may also occur). Mating takes place during a postpartum estrus about three weeks after birth between the dominant male and female.
The dominant female is the only member of the group that produces offspring. The presence of an adult female may suppress ovulation in other female members of the family. Gestation lasts 4.5 months. After the first 24 hours, young are most often carried by the adult male or juveniles and returned to the adult female for nursing. This practice relieves the energy drain on the mother and gives siblings practice for parenthood.
At birth the young weigh approximately .5 ounces (15 g). An individual nurses until about three months and is sexually mature by one to 1.5 years. They generally reach adult size by age two. Juveniles usually stay with the group through two subsequent birth cycles.
Pygmy marmosets live into their early 20s in zoos; their life span in the wild is about 11 to 12 years.
Diet in the Wild
Pygmy marmosets are gumophores, which means that they gouge holes in trees and feed primarily on tree sap or gum. They also eat insects, small lizards, spiders, and some fruits. In fact, 67 percent of their feeding time is spent eating tree exudates or preparing new food sources by gnawing tree trunks or large branches, from which they will later collect sap.
Gums are particularly important for pygmy marmosets because their home ranges are so small that they cannot rely on fruit year round. As an adaptation for gnawing, marmosets have long, forward turned, lower incisors that are the same length as their canines; this is the case in all marmosets and is termed the short-tusked condition. (Tamarins, another group of small monkeys, have lower canines that are longer than their lower incisors.) They also have two molars as opposed to three in most other monkeys.
Pygmy marmosets are currently not endangered. However they are listed as special concern or somewhat threatened. Because of their size, mobility and coloration, it is almost impossible to count the pygmy marmosets living in the South American forests. A threat to these small monkeys is the pet trade.
The main predators of the pygmy marmoset are birds of prey. These monkeys are flexible and adapt to environmental changes caused by humans. For example, they have been found living in small groups of trees on the edges of farms that have been created by clear cutting. They have also been known to use secondary forest habitats if there is suitable food available.