Common Marmosets
Due to the small size of marmosets and tamarins, they are often referred to as “miniature monkeys”. Did you know that these monkeys “tan”? The skin on their face changes colour in the sun and it even seems like they get freckles!

Physical Description: Common marmosets are a mix of brown, grey and yellow colours. Their long tails have an interesting banded coloration. Marmosets are born without their characteristic white ear tufts and develop these by adulthood. Adult males average 188mm in height and 256g for weight. Adult females are slightly smaller at 185mm and 236g on average. Marmosets have many special physical traits that are tailored to their lifestyle. Since they do a lot of clinging and leaping, they have claw-like nails called tegulae instead of flat nails. They also have special incisors as well as a specialized part of the large intestine to accommodate their diet. The lifespan for the common marmoset is 12 years in the wild.

Habitat: Common marmosets are found naturally in the northeastern and central forests of Brazil. They do well in dry secondary and disturbed forests as well as edge habitats, but they can also live in other forest types such as savannah forest (called cerrado), riverine forest, coastal forest, thorn scrub habitat (called caatinga) and semideciduous inland forest. Marmosets are arboreal and quadrupedal. They can also leap quite far and cling vertically to branches.

Diet: Common marmosets are exudativore-insectivores. This means that their primary diet consists of exudates like gum, sap, and resin as well as insects which provide protein and fat. Marmosets also eat fruit, seeds, flowers, fungi, nectar, snails, lizards, tree frogs, nestlings and infant mammals. Marmosets are not high-distance travellers like some other primate species. On average they only travel 0.5–1.0km a day. They are usually active shortly before and after sunset (11–12 hours per day).

Life History: Gestation in the common marmoset is 143-153 days. Common marmoset females can have 1–3 infants at a time. Twins are common and are often non-identical which is atypical for primates. Females give birth twice a year. Twin infants can be up to 27% of the mother’s body weight when they are born. It would be nearly impossible for the mother to rear offspring on her own. Instead, infants are raised by the entire group in a practice known as collective rearing. Infant marmosets remain with a caregiver constantly during the first 2 weeks of life. Infants are weaned around 3 months of age. The juvenile period begins at 5 months. At this stage marmosets are approximately 75% of their adult weight. The sub-adult stage begins between 9–14 months of age. Common marmosets reach their adult weight and are sexually mature by 15 months, but they do not reproduce until environmental conditions are favourable.

Associations: There are no known associations in the wild, but there are reports of marmosets being successfully paired with rodents and birds in captivity. However, the Monkeyland marmosets were unable to live peacefully in our sister sanctuary, Birds of Eden. They are also too small to live in our forested area. We are now working on a project to make a special enclosure for them.

Social Structure: The average group size for the common marmoset is 9 individuals, although groups can range anywhere from 3–15 individuals. It is difficult to study marmosets in the wild, so there is some uncertainty regarding their social structure. Groups tend to be stable and consist of an extended family unit. Females in a group are often related. Males are thought to emigrate from their natal group as adults, likely in search of mating opportunities. Within each group there are a few dominant breeders. These individuals suppress breeding in subordinate group members. The hierarchy for the subordinate, non-breeding individuals is determined by age. Subordinates contribute to the group’s overall fitness by helping to rear infants. In the event that a breeding individual dies, the group will subdivide.

Communication: Common marmosets have scent glands on the chest and in the anogenital region. They use these scent glands to mark their territory, as well as to communicate their social and reproductive status. Common marmosets have what has been termed a “second nose” (officially called the vomeronasal organ) for olfactory communication.

The vomeronasal organ is an internal structure also present in humans! Common marmosets use facial expressions, postures, vocalizations and olfaction to communicate. These communicative behaviours have been given descriptive names. They include the “partial open mouth stare” which signifies alarm and the “slit-stare” and “(ear) tuft-flatten” which mean submission. A “frown” means aggression.

Vocalisations include alarm calls and general calls. Two types of alarm calls are “staccatos” and “tsiks”. Marmosets use alarm calls to warn group members of a predator. They may also be used to solicit a group mobbing response. One general vocalisation is the “phee” call which resembles a loud whistle and is used in long distance communication. Another type of general call is the “trill” which is used primarily to identify conspecifics.

Mating: Mating is flexible in common marmosets. The majority of mating is thought to be monogamous but polygyny (one male with several females) and polyandry (one female with several males) have also been observed. Mating is largely determined by suitable social conditions. Although marmoset females have a cycle length comparable to humans (average 28 days), they do not menstruate.

Subordinate females cycle but are suppressed from breeding. The mechanisms of this suppression however are not understood. Females will flick their tongues at males to attract a mate. Females are able to mate at any time but the majority of copulations occur around the time of their ovulation. Within 10 days of giving birth, females are able to cycle and become pregnant again. Females give birth every 5 months approximately. In the wild, births are timed around the rainy/dry seasons and food availability.

Other Behaviour: A typical day for the common marmoset consists of an hour of heavy feeding in the morning followed by alternated periods of resting, foraging and socializing. Marmosets sleep huddled together at night, possibly as a mechanism for avoiding predators like large cats, raptors, larger monkeys and arboreal snakes. At Monkeyland, common marmosets have been known to urinate on guests so be careful around these little ones!

Unfortunately, the common marmosets we released into Birds of Eden did not get on with the birds very well, so we have to find a new solution. A separate large enclosure will be built for them, but for now they live in family groups in cages that we try to make as exciting for them as possible by giving them lots of natural materials (e.g. plants and branches) and enrichment devices (e.g. water features and toys).

Sadly, it’s hard to keep up since they are such common pets and many people grow tired of keeping them at home. Their tiny bite can be surprisingly painful and they like to urinate everywhere!

Conservation: Common marmosets are classified as Lower Risk/Least Concern by the IUCN. This means that there is currently a viable population in the wild and although habitat loss is occurring, threats to this species have not reached a critical point yet. As much as 80% of the natural range of the common marmoset has been razed for agriculture.

Marmosets are also commonly captured and sold into the pet trade. When primates become pets, they are often fed junk food and sweets, and do not get proper animal care. A common complaint heard at Monkeyland from prior owners of marmosets is that their marmoset urinated on everything in the house. This behaviour is natural for the marmoset to mark its territory, but a very undesirable pet behaviour. It is not known how many marmosets are being kept worldwide as pets. Common marmosets are also the most widely used non-human primate in research in Europe.

Brazil banned the export of common marmosets in 1974, so marmosets being used in research since this time have come from captive breeding colonies. Sanctuaries involved in marmoset conservation such as the Sonora Desert Primate Conservancy (USA) maintain a captive population with the aim of reintroducing marmosets to the wild in the near future.

Other organisations working to promote marmoset conservation include Fundacion Vida Silvestre Argentina (Argentina;
www.vidasilvestre.org.ar), Jungle Friends Primate Sanctuary (USA; www.junglefriends.org) and the Pacific Primate Sanctuary (USA; www.pacificprimate.org).

Please visit their websites for more information on the common marmoset and current
conservation efforts.

Did You Know?
During resting, common marmosets are capable of remaining completely motionless for over 30 minutes!