Squirrel Monkeys
It was originally thought that there were just two species of squirrel monkey. Due to recent genetic advances, we now know there are at least five. These are classified into two main groups: Saimiri sciureus, which includes the common squirrel monkey and Saimiri boliviensis, which includes the Bolivian squirrel monkey. Both can be found in the Monkeyland forest.

Physical Description: Squirrel monkeys in general are grey with bits of red-orange fur and yellow-orange arms, hands, and feet. They have tufts of white fur on their ears as well as white fur around their eyes. There is also a circle of brown-black fur surrounding their mouths. The weights and heights of common and Bolivian squirrel monkeys
are very similar.

The common squirrel monkey male weighs 554–1150g and is approximately 318mm long. Females weigh around 651–1250g and are approximately 316mm long. Bolivian squirrel monkey males and females are both about 310mm long. Females tend to weigh 700–900g and males around 963–1088g. Males of both subspecies can gain almost a quarter of their own body weight to impress females!

There are two key physical differences that can be used to distinguish these species from one another. Common squirrel monkeys have a “gothic” arch where the fur on their forehead forms a deep “V” between their eyes compared to Bolivians which have a shallow “V” known as a “roman” arch. The latter also have thinner tails compared to common squirrel monkeys. As a visitor to Monkeyland, chances are you will see Bolivian squirrel monkeys as they are much more abundant in our forest.

Habitat: Squirrel monkeys are found primarily in the tropical lowland rainforest of the Amazon, although they easily adapt to other forest types. The range of common squirrel monkeys encompasses such countries as Brazil, Colombia, French Guiana, Guyana, Suriname and Venezuela.

Bolivian squirrel monkeys are found in Bolivia, as well as Brazil and Peru. Squirrel monkeys are quadrupedal and arboreal. They tend to prefer small branches that are 1–2cm thick. Unlike Monkeyland’s black and white ruffed lemurs that can leap distances of 15m or more, squirrel monkeys are not leapers by nature and tend to only leap distances of 2m or less.

Diet: Squirrel monkeys are insectivores-frugivores, so the majority of their diet is made up of insects and fruit. They are particularly fond of caterpillars and grasshoppers. They will also eat small vertebrates such as birds and bats as well as foliage, seeds and gum.

Between-group aggression over feeding sites has been observed in wild common squirrel monkeys, but not in the Bolivian squirrel monkey. This is likely due to differences in food availability in the different subspecies’ habitats. Squirrel monkeys in general rest only 10% of their day. The majority of their time is spent looking for food (50% looking for insects,
10% eating fruit).

Life History: Squirrel monkey infants are born after a 145 day gestation period and births are often synchronized within the group to minimize predation. Infants are cared for almost exclusively by females. Common squirrel monkey males defend infants from predators, but Bolivian squirrel monkey males do not. Squirrel monkey infants are carried on the mother’s back.

After about a month, infants will begin to explore away from the mother and will become independent between two and four months of age. Bolivian squirrel monkeys have been observed to nurse infants for up to 18 months of age, while other subspecies tend to wean their infants earlier. The average lifespan of the squirrel monkey is 20 years.

Associations: Squirrel monkeys have many predators because they are quite small. Their biggest threat comes from raptors, although they are also preyed upon by snakes and large cats. Squirrel monkeys often associate with other nonhuman primate species in the genus Cebus such as capuchins. Squirrel monkeys can take advantage of the capuchin alarm calls to avoid some of their predators and may also gain greater access to food resources through these associations.

Social Structure: Although other characteristics of squirrel monkeys are similar, social organization varies considerably between subspecies and geographic regions. Common squirrel monkeys observed in Suriname live in integrated multi-male/multi-female groups of 15–30 individuals. There is a dominance hierarchy in males and in females.

Aggression is quite common. Males in this subspecies tend to associate, often forming bonds with others, while females do not. Both sexes leave the group they were born in and transfer into new groups. In comparison, Bolivian squirrel monkeys studied in Peru were found to live in larger groups, with multi-male/multi-female group sizes of 45–75. Only the males in this subspecies leave the group they were born in.

This occurs when they are sexually mature. Males often form similar-age coalitions and work together to transfer into new groups and challenge dominant males. Once in a new group, coalitions also work together to try to keep out new intruders. There is a dominance hierarchy within females as well and in general they are dominant over males. Females tend to keep males in the group’s periphery and are also aggressive to unrelated females.

Scent Marking: Squirrel monkeys use olfactory cues and postural displays to mark their territories. They have scent glands on their chest and in their anogenital region, used to mark other squirrel monkeys or objects in their environment such as branches. They are also known to utilize scent cues by rubbing their nose along something and then sneezing into their hands! Another interesting behaviour related to olfaction is “urine-washing”. Both sexes engage in this postural display. A monkey will urinate on its hands or feet and then rub the urine all over its body. The exact function of this behaviour is unknown. Possible reasons may be self-cleaning, trail-marking or displaying dominance.

Other Communication: Perhaps one of the most diverse method of primate communication is the squirrel monkey’s vocal repertoire. There are at least 25 different vocalizations. These are classified as either “chucks”, “pulsed calls”, “cackles”, “noisy calls”, “peeps” or “twitters”. Of these six subgroups, the most common type of call is “chucks”. “Chucks” are used in many contexts, including mating and situations of alarm.

The “pulsed” class of calls sounds different than “chucks” but is used similarly. “Cackles” signal a minor problem whereas “noisy calls” signal a major problem. “Peeps” and “twitters” are both used in exploration as well as other contexts. One specific call, the yap, is used to signal a mammalian predator and is used by the group as a
mobbing defence.

Mating: Squirrel monkeys have a polygamous mating system that is dominated by one or two top males. Experienced females will choose the males who have become the largest in size, while inexperienced females are not as picky. Females become sexually mature at 2.5 years of age, which is about a year earlier than males.

Other Behaviour: Squirrel monkeys at Monkeyland have been known to associate with some of our spider monkeys. Mrs. Bean (squirrel monkey) and Tarzan (spider monkey) have often been spotted grooming each other. Another spider monkey, Jane, has become a surrogate mum to some of our orphaned squirrel monkeys.

Conservation: The common and Bolivian squirrel monkeys are listed as Lower Risk/Least Concern by the IUCN. Other subspecies of squirrel monkey, however, are Critically Endangered. Like other primates, squirrel monkeys face habitat destruction from human abuse of the forest.

They are threatened by advancing agriculture, logging, and the expansion of human settlements. Squirrel monkeys are also used heavily in captive research. Only rhesus monkeys are used more than squirrel monkeys. Finally, squirrel monkeys are one of the most popular primates to be kept as pets. Often they are captured illegally and smuggled to domestic and foreign markets.

Squirrel monkeys are meant to be wild animals. They can and will bite, defecate, and destroy property at will. When pet primates develop these negative behaviours, they often become unwanted and homeless. Monkeyland does not condone the keeping of primates as pets! Please be a part of spreading this message and helping to change the general attitude towards the primate pet trade.

Did You Know: The squirrel monkey is the smallest species in the Monkeyland forest and also the most numerous. Squirrel monkeys are found in groups and you will almost never see one without a friend nearby. If you’re at Monkeyland during mating season, you can see bulky males strolling around trying to impress the females! Males can gain up to 20% of their body weight from storing water and fat.