It is a small monkey with an orange back and a distinctive white and black facial mask.

It has an omnivorous diet, eating fruits, other plant materials, invertebrates and some small vertebrates.

[7][8] The binomial name Saimiri oerstedii was given by Johannes Theodor Reinhardt in honor of his fellow Danish biologist Anders Sandøe Ørsted.

There are two subspecies of the Central American squirrel monkey:[1] S. o. oerstedii lives in the western Pacific portion of Panama and the Osa Peninsula area of Costa Rica (including Corcovado National Park), while S. o. citrinellus lives in the Central Pacific portion of Costa Rica.

[4] Adults reach a length of between 266 and 291 millimetres (10+1⁄2 and 11+1⁄2 inches), excluding tail, and a weight between 600 and 950 grams (21 and 34 ounces).

[12][13] The Central American squirrel monkey is arboreal and diurnal, and most often moves through the trees on four legs (quadrupedal locomotion).

[14] Group ranges can overlap, especially in large, protected areas such as Manuel Antonio National Park.

[16] The group tends to sleep in the same trees every night for months at a time, unlike other squirrel monkeys.

[14] Neither males nor females are dominant over each other, an egalitarian social system that is unique to Central American squirrel monkeys.

[6] Groups of Central American squirrel monkeys generally do not compete or fight with each other.

[20] In one study a slight tendency was observed in which Central American squirrel monkeys were more likely to travel near mantled howler monkeys if the howlers were vocalizing loudly within their home range, but no physical contact or obvious social interaction was observed.

At Corcovado National Park, bird species known to regularly follow squirrel monkeys include the double-toothed kite, the grey-headed tanager and the tawny-winged woodcreeper, but other woodcreepers and such species as motmots and trogons do so as well.

It also eats small vertebrates, including bats, birds, lizards, and tree frogs.

It finds its food foraging through the lower and middle levels of the forest, typically between 4.5 and 9 metres (15 and 30 feet) high.

It has difficulty finding its desired food late in the wet season, when fewer arthropods are available.

[9] Predators of the Central American squirrel monkey include birds of prey, cats and snakes.

[2][14] When a Central American squirrel monkey detects a raptor, it gives a high-pitched alarm peep and dives for cover.

The monkeys are particularly cautious about raptors, and give alarms when they detect any raptor-like object, including small airplanes and even falling branches and large leaves.

This may be because the most enlarged males are generally the oldest and the most effective at detecting predators, or it may be a case of runaway intersexual selection.

The gestation period is six months, and the infants are born within a single week during February and March.

[6] The lifespan of the Central American squirrel monkey in the wild is unknown, but captive specimens have been known to live more than 15 years.

[6] The Central American squirrel monkey has a restricted distribution in Costa Rica and Panama.

Its range covers Central Pacific Costa Rica in the north through western Panama.

[4] A genetic study by Lynch Alfaro, et al. in 2015 estimated that the Central American squirrel monkey diverged from S. scuireus a little less than 1 million years ago.

[8] One popular theory is that squirrel monkeys did live in Colombia during the late Miocene or Pliocene and these squirrel monkeys migrated to Central America, becoming the ancestors of the current Central American species.

Passage through the isthmus of Panama later closed due to rising oceans, and eventually opened up to another wave of migration about 2 million years ago.

These later migrants, ancestors to modern populations of white-headed capuchins, mantled howlers and Geoffroy's spider monkeys, out-competed the earlier migrants, leading to the small range of the Central American squirrel monkey and Guatemalan black howler.

[24] As of 2021, the Central American squirrel monkey is listed as endangered from a conservation standpoint by the IUCN.

[2] This is due mainly to deforestation ongoing habitat loss, but other sources such as capture for the pet trade also contribute.