Squirrel monkey quick facts
- For its body size, the squirrel monkey has the biggest brain of any primate: about one part in seventeen.
- The tail is a balance pole, not a hand. Squirrel monkeys cannot hang by it.
- Troops usually hold 45 to 75 monkeys, and sometimes join up into super-troops of more than 100.
- Almost every baby in a troop is born within the same few weeks of the rainy season.
- The Central American squirrel monkey is Endangered; the Bolivian squirrel monkey is Least Concern.
What is a squirrel monkey?
A squirrel monkey is a small monkey from the warm forests of Central and South America. Scientists group them in the genus Saimiri. They belong to a big family called the New World monkeys. Those are the monkeys of the Americas. Their cousins include the spider monkey and the howler monkey.
You can spot one by its face. The fur around the eyes and nose is pale, almost white, and the muzzle is black. People often say it looks like a tiny clown mask. The back and arms are a warm olive or orange. The hands and feet are a brighter yellow-orange. That golden colour is why some people call them golden monkeys.
A squirrel monkey is not much bigger than a pet cat, and most of what you see is tail. The body is about 25 to 35 cm long. That is a school ruler and a bit more. The tail adds another 35 to 42 cm on top of that. A grown-up weighs about 750 g to 1.1 kg. You could hold one in two hands, if it let you.
Why the tail is not for swinging
Plenty of monkeys hang from their tails. Squirrel monkeys cannot. Their tail is not prehensile. That is the word for a tail that can grip like a hand. Instead it works as a balance pole, the way a tightrope walker holds a long stick.
That one difference changes how they move. A spider monkey swings from branch to branch under the canopy. A squirrel monkey runs along the top of branches and leaps the gaps, which is much more like a squirrel — and that is where the name comes from. A young one curls its tail around its mother while it rides on her back. It will never trust that tail to hold its whole weight.
Where do squirrel monkeys live?
Squirrel monkeys live in tropical forest. Their range runs from Costa Rica in the north down through the Amazon rainforest of Brazil, Peru and Bolivia. They like the middle layers of the forest, not the very top. They are fond of the trees along rivers and in places that flood, where branches grow thick and low.
Those riverside forests suit them. Food is easy to reach, and there is somewhere to hide. A troop rarely goes down to the ground for long. High among the leaves there is fruit, there are insects, and there is cover from eagles.
What do squirrel monkeys eat?
A squirrel monkey eats mostly fruit and insects. It spends close to half of every day looking for them. Small soft fruits and figs are favourites. So are grasshoppers, caterpillars, spiders and beetles. They pick them out of curled-up leaves with quick fingers.
The mix changes with the seasons. In the drier months, from about June to December, ripe fruit is harder to find. The troop then eats far more insects. They also take flowers, nectar, buds, small frogs, lizards and eggs. This monkey is not fussy. Being able to switch foods is part of why it does well.
| Fact | Squirrel monkey |
|---|---|
| Scientific group | Saimiri, a New World monkey |
| Body length | About 25–35 cm, plus a 35–42 cm tail |
| Weight | About 750 g to 1.1 kg |
| Home | Forests of Central and South America |
| Main foods | Fruit and insects |
| Troop size | Often 45–75, sometimes more than 100 |
| Life span | Up to about 15–20 years in the wild |
Living in a big noisy troop
Squirrel monkeys are some of the most social monkeys there are. A troop of Bolivian squirrel monkeys usually holds 45 to 75 animals. Now and then smaller groups join into a super-troop of more than a hundred. Moving in a crowd that size makes it much harder for a hunter to pick one animal out.
The females are in charge. They stay in the group they were born into, and they keep the best feeding spots. Adult males are pushed out to the edge of the troop. A male who wants a place near the centre puts up with a lot of shoving.
The troop talks constantly. Scientists have counted more than twenty different calls. There are peeps, cackles, chirps and trills. One call warns the others that an eagle is overhead. Another says a hunter is on the ground. A mother and her baby have quiet sounds for finding each other in thick leaves.
Babies and growing up
Babies arrive together. Almost all the females in a troop give birth inside a few weeks of each other. It happens in the rainy season, between about December and May. With every baby arriving at once, no single infant is an easy target. It also lines the births up with the months when fruit is easiest to find.
A newborn clings to its mother’s back straight away and rides there for weeks. Other females in the troop help carry and watch it. You do not see that in every monkey. Females are grown up at two to three years old. Males take four to five. In the wild a squirrel monkey can live 15 to 20 years.
How clever is a squirrel monkey?
Here is the fact that surprises most people. For its size, a squirrel monkey has the biggest brain of any primate on Earth. Its brain weighs about one part in every seventeen parts of its body. In a human the figure is roughly one part in thirty-five. That does not make a squirrel monkey cleverer than you. Brains are not that simple. It is still a striking number.
You can see the cleverness in the way they feed. They remember which trees fruited last month. They go back at the right time. They pull apart rolled leaves to find hidden insects. They work out how to reach food that is behind something else. Youngsters copy the tricks the adults use.
Who hunts a squirrel monkey?
A small monkey in a big forest has a lot to worry about. From the air, the danger is harpy eagles, crested eagles and black-hawk eagles. On the branches, boa constrictors and anacondas lie still and wait. On the forest floor, jaguars and ocelots hunt anything they can catch.
This is why the alarm calls matter. Seventy pairs of eyes beat seven. One monkey spots a shape in the sky and gives the eagle call. The whole group drops into cover.
Are squirrel monkeys endangered?
It depends which one you mean. There are several species, and they are not all in the same trouble.
The Bolivian squirrel monkey of the upper Amazon is listed as Least Concern, which means it is not thought to be at risk right now. The Central American squirrel monkey, the orange-backed one from the Pacific coast of Costa Rica and Panama, is a very different story. It is listed as Endangered. Its forest has been cleared for farms, cattle and palm oil. What is left is broken into patches monkeys cannot easily cross.
There is some good news attached. In Costa Rica, people have built rope bridges across roads so troops can cross safely. Protected forest at Manuel Antonio and Corcovado gives them somewhere to live. Squirrel monkeys also belong in the ecosystem as seed spreaders: fruit goes in, seeds come out somewhere else, and new trees grow.
Three things people get wrong
“They swing through the trees by their tails.” They cannot. The tail is for balance, not for gripping.
“They would make a fun pet.” They would not, and in most places keeping one is against the law. A squirrel monkey needs a troop of dozens and a whole forest to search. Its diet is not something you can buy in a shop. The pet trade is one reason some species are in trouble.
“A monkey is a monkey.” There are several squirrel monkey species. Telling them apart is a real job for scientists. The neatest clue is the pale mask. Some species have a high, rounded arch above the eyes. Others have a low, pointed one.
Did you know? Squirrel monkeys have more than twenty different calls, and one of them means “eagle” while another means “danger on the ground”. The troop reacts differently to each.
Try it
Measure 30 cm on a ruler for the body, then 40 cm for the tail. Lay them end to end on the floor. That is one squirrel monkey, and most of it is tail.
Knowledge check
Why can a squirrel monkey not hang from its tail?
Show answer
Its tail is not prehensile, so it cannot grip. The monkey uses it as a balance pole while it runs and leaps along branches.
Why are all the babies in a troop born at the same time?
Show answer
Predators cannot single one baby out when dozens appear at once, and the births line up with the rainy season, when fruit is easiest to find.
Frequently asked questions
How big is a squirrel monkey?
The body is about 25 to 35 cm long and the tail adds another 35 to 42 cm. A grown-up weighs roughly 750 g to 1.1 kg.
What do squirrel monkeys eat?
Mostly fruit and insects. In the drier months, from about June to December, they eat far more insects because ripe fruit is harder to find.
How long do squirrel monkeys live?
Up to about 15 to 20 years in the wild. Monkeys in zoos, where there are no eagles or jaguars, often live longer.
Can I keep a squirrel monkey as a pet?
No. They need a troop of dozens and a whole forest to search, keeping one is illegal in most places, and the pet trade is one reason some species are endangered.
Are squirrel monkeys endangered?
Some are. The Central American squirrel monkey is listed as Endangered after its forest was cleared for farms and palm oil. The Bolivian squirrel monkey is listed as Least Concern.
Why is it called a squirrel monkey?
Because of how it moves. It does not swing under branches like a spider monkey. It runs along the top of them and leaps the gaps, much the way a squirrel does.
Sources
- New England Primate Conservancy: Bolivian squirrel monkey — size, weight, diet, troop size, birth season, predators, calls and life span
- New England Primate Conservancy: black-crowned Central American squirrel monkey — the Costa Rica and Panama range, forest loss and the population decline
- IUCN Red List: Saimiri oerstedii — the Endangered listing for the Central American squirrel monkey
- Animal Diversity Web, University of Michigan: Saimiri oerstedii — the non-prehensile tail, feeding behaviour and social structure
- London Zoo: black-capped squirrel monkey — the brain-to-body figure of about 1:17 and the comparison with humans
