Saimiri sciureus

Geographic Distribution and Habitat

Guianan squirrel monkeys (Saimiri sciureus) are endemic to the tropical forests of French Guiana, Guyana, Suriname, and Brazil. They occupy many forest types, generally preferring primary and secondary forests. They may venture to the forest floor or explore the upper reaches of the canopy, but they spend most of their time in the rainforest’s food-rich and well-protected middle canopy.


Until very recently, Saimiri scuireus was commonly called the “common squirrel monkey.” The common squirrel monkey had a very broad geographic range throughout South America’s Amazon Basin. In 2015, genetic research conducted throughout that range revealed that there were, in fact, four distinct squirrel monkey species under the umbrella classification S. scuireus, or common squirrel monkey. They are the Guianan squirrel monkey (S. scuireus), described here, Humboldt’s squirrel monkey (S. cassiquiarensis), Collins’ squirrel monkey (S. collinsi), and the Ecuadorian squirrel monkey (S. cassiquiarensis macrodon).

The distinctions were formally announced in April 2020 and work is still being done to describe the differences between and among the species. Thus, the commonly used “common squirrel monkey” moniker is obsolete, but old habits die hard and it will be some time before that term goes away. All four species will surely be referred to as “common squirrel monkeys” for some time to come. To confuse things further, there are virtually no visible physiological differences between the species. As well as DNA, geographic location distinguishes the species. ​Furthermore, such recent taxonomic restructuring means that the subtle differences between these species are still coming to light.

Guianan squirrel monkey geographic range, IUCN 2020

Size, Weight, and Lifespan

Squirrel monkeys weigh 32.6 ounces (925 grams) on average. They have small and slender bodies about 12.5 inches (31.75 cm) long, and tails that add an extra 16 inches (40 cm). They can live up to 15 years in the wild.


Squirrel monkeys have small compact bodies and long tails. Despite its length, the tail is not prehensile. Although it is not capable of grasping objects, it does provide exceptional balance and poise as they move nimbly—not unlike a squirrel—through the trees. Their tiny hands are equipped with nails, not claws, which enhance their ability to grasp and cling.

The squirrel monkey’s pelage or coat is primarily gray in color. However, the fur on their legs is bright yellow. Yellow fur also mixes with the gray fur on their torso and the top of their head. Their pointed ears are wreathed with white fur and white fur encircles their dark eyes.

Squirrel monkeys are not outrightly sexually dimorphic. Males do sport larger upper canines than females, however.

Although some squirrel monkey species differ slightly in color placement and the shape of the black cap on their heads, the newly defined Guianan squirrel monkey species have not been described as having any major morphological features that distinguish them from other species of squirrel monkeys.


Squirrel monkeys primarily eat fruit. However, they may settle for leaves and seeds when fruit is not available. On occasion, they hunt insects, arthropods, and even small vertebrates like bats and birds.

The specific staples of Guianan squirrel monkeys’ diet, if they differ at all from the other “common squirrel monkeys,” are not yet available.

Behavior and Lifestyle

Though they may venture to the ground to play or to forage for food on occasion, squirrel monkeys are strictly arboreal (tree-dwelling). Their small bodies and long tails give them the uncanny ability to scurry along branches, on all fours, with unwavering agility. As they go, they use their nimble fingers, equipped with fingernails, to climb. These also help them break into the delicious fruits they forage.

They are gregarious and social monkeys, living in a large and dynamic group. In between feedings, this group stops to rest and socialize. Adults groom each other and young monkeys play together.

Fun Facts

The Guianan squirrel monkey’s scientific name, Saimiri sciureus, formerly referred to the common squirrel monkey, a label no longer in official use.

Squirrel monkey species are barely visibly different from each other, a fact that made accurate classification of them nearly impossible prior to the advent of genetic sequencing.

Squirrel monkeys have one of the slowest reproductive rates of any primate, making them particularly affected by illegal poaching.

Daily Life and Group Dynamics 

Squirrel monkeys live in groups of up to 300 members. By traveling, foraging, socializing, and sleeping together in such large numbers, they protect themselves and their resources from potential rivals. Occasionally, however, it is more convenient for a few group members to form a smaller troop and break off from the large group temporarily.

Their groups are composed of multiple males and females, with females taking the main dominant positions. Males operate according to their own hierarchy that, to some degree, determines who is allowed to mate. But with so many members in one group, who could possibly keep track?

Squirrel monkeys sometimes mingle with groups of capuchin monkeys. Capuchins tend to make more alarm calls, and are more vigilant about watching for predators than squirrel monkeys. Thus, by learning when capuchins are sounding the alarm, squirrel monkeys give themselves more chances to escape from dangerous predators.


Like many socially driven primates, squirrel monkeys have developed ways to communicate with each other.

A squirrel monkey can make a number of alarm calls, which he uses to warn others of an approaching threat. The call he makes even lets his group know what kind of predator is nearby, allowing them to prepare accordingly.

Though not aggressively territorial, squirrel monkeys do use scents to mark their territories or to leave a trail for other group members to follow.

Reproduction and Family

Squirrel monkeys are known for being a particularly promiscuous species of primate. Though there is a hierarchy amongst males that determines who of them has the right to mate first, the considerable size of their group makes regulating and enforcing these conventions difficult.

Mating happens during September and November. After five to seven months, the mother gives birth. By that time, the rainy season is well under way, meaning fruit is ripe and plentiful. The mother acts as her infant’s exclusive caretaker, nursing and carrying him or her as the group travels between feeding sites. Older females without offspring may offer her help from time to time.

Females reach maturity, at three years old—earlier than males, who are not fully mature until five years old. Males also go through a sub-adult period in which they are essentially mature but still play regularly with younger monkeys.

Ecological Role

Squirrel monkeys play important roles in their local ecosystems, dispersing seeds and keeping insect populations in check.

Conservation Status and Threats

The Guianan squirrel monkey is listed as Least Concern by the International Union for Conservation of Nature (IUCN, 2020) appearing on the IUCN’s Red List of Threatened Species. Even so, populations of Guianan squirrel monkeys are currently in decline.

Squirrel monkeys are fortunately too small to be good hunting for humans. However, their long history of being kept as pets, and for biomedical research, has adverse effects on their populations—not to mention the welfare of individuals who find themselves in captivity. Squirrel monkeys are extremely social creatures. The freedom they require to lead a happy life can only be found in their natural environment, living among their own kind.

While trafficking squirrel monkeys is illegal in some countries, owning one is another story. Poachers, who don’t care one way or another, often kill a mother in order to take her infant to sell on the black market. Many buyers do not realize this—nor just how painstaking caring for a squirrel monkey is. As a result, many monkeys bought as pets wind up in animal rehabilitation centers.

Once brought up in captivity, however, reintroducing a squirrel monkey to the wild is not an easy task. A monkey taken from the wild as a helpless infant never learned the skills she needs to survive in her natural environment. It is then up to rehabilitators to teach her those skills.

The focus on killing mothers in order to poach infant monkeys to sell as pets has adverse downhill effects on squirrel monkey populations. Most significant of these is that the death of a mother, and the capture of her offspring, means the removal of an entire potential lineage from the wild. The more that genes are culled in this way, the more likely squirrel monkey populations will suffer from genetic bottlenecks that gradually make wild populations less viable overtime.

Though adaptable, squirrel monkeys are still harmed by the patterns of deforestation and forest fragmentation happening in the places they call home. As forests are converted into farmland, or become divided by roads and other human infrastructure projects, monkeys lose access to important food sources as well as to each other.

Conservation Efforts

Specific conservation efforts for wild squirrel monkeys are few and far between. The recent taxonomic changes to this genus will hopefully breathe new life into research and conservation of the Guianan squirrel monkey, as well as other varieties. Understanding the subtle differences between these species could make all the difference when it comes to conserving them.

Due to their prevalence in the exotic pet trade, it is not uncommon for many squirrel monkeys to end up in rehabilitation centers. Today, there are many sanctuaries, all over the world, that specialize in caring for rescued squirrel monkeys. These are a mixed blessing, however. Though a former pet squirrel monkey is certainly better off in the hands of people who can care for him properly, the process of rehabilitating him is complicated and not often successful. Therefore, educating people about the cruelty, and selfishness, of keeping primates as pets is a crucial part of ensuring their survival in the wild.


Written by Zachary Lussier, January 2021