Saimiri vanzolinii

Geographic Distribution and Habitat

The black-headed squirrel monkey, also called the black squirrel monkey, is limited in geographic range to the várzea forest within the Mamirauá Sustainable Development Reserve in Brazil. They occur exclusively in flooded forests and have the smallest geographic distribution of any known Neotropical primate.

They specifically prefer river-edge, seasonally inundated, and secondary forests, and are predominantly found traveling and foraging in the medium and lower strata of the forest canopy. They rarely venture up to higher levels of the canopy or to forest clearings to avoid being seen by predators. 

Black-headed squirrel monkey geographic range. Map: IUCN, 2008
Size, Weight, and Lifespan

Although both male and female black-headed squirrel monkeys are identical in appearance, they are seasonally sexually dimorphic. An average male’s weight increases during the two months prior to breeding season, which makes him appear “fattened,” or healthy, and is attractive to females. Males weigh about 1.4–2.7 lbs (649–1225 g), while females are just under that, at 1.4-1.9 lbs (649-898 g). Head-to-tail length for males and females ranges anywhere from 11 to 13 in (27–32cm).

Black-headed squirrel monkeys live around 15 years in the wild, and around 20-25 years when in captivity.


Black-headed squirrel monkeys are small primates with dark eyes that are outlined by a round-shaped mask of white hair. The short dense coat on their back is blackish-gray, while their forearms, limbs, and underbelly are yellowish in hue. Their ears and throat are white, and the skin around their lips and nostrils is black and hairless. They get their name from the strip of black that extends from their head to the end of their tail. The black hair above their eyes forms a shallow arch and is lower on their foreheads than other squirrel monkey species. This is one of the major distinguishing traits that differentiates them from other squirrel monkey species.

Their long, slim tails, which are narrower than those of other squirrel monkey species, are used for balancing when climbing branches, and are twice the length of their bodies. The tip of their tail is a dark color and is far bushier than the rest of it.


Black-headed squirrel monkeys are omnivorous and feast upon plants as well as small animals. Other items on their menu include fruit, insects (most preferably grasshoppers and caterpillars), flowers, seeds, eggs, lizards, nuts, buds, and other small vertebrae. Shortages of fruit during high season result in a heavier reliance upon animal prey.

Behavior and Lifestyle

Black-headed squirrel monkeys are diurnal (active during daylight hours) and arboreal (tree-dwelling) creatures and have the ability to move about the trees with exceptional speed. They can leap horizontal distances greater than 6.5 ft (2 m). More than half of their day is spent searching for insects and fruit, while the remainder is reserved for grooming and socializing. While grooming is often a social activity for primate species, black-headed squirrel monkeys self-groom.

Fun Facts

Of all the New World primate species, squirrel monkeys have the largest brains in proportion to their bodies, whereas capuchin monkeys have the largest brains in relation to their body weight.

They are sometimes called the “death’s head monkey” because of their black-and-white faces.

Female squirrel monkeys have a “pseudo-penis,” which is a significantly large clitoris that resembles a male penis. Females will show this off to express dominance over other females in a troop.

Daily Life and Group Dynamics 

They are highly social creatures that live in large troops of approximately 40 to 50 individuals but can contain up to as many as 500 members.

To increase protection against neighboring threats, they form temporary and peaceful alliances with other primates in the forest, such as capuchins.


Common forms of communication among squirrel monkeys include vocalizations and olfactory tactics.

There are between 25-30 different vocalizations used to communicate with the rest of the troop, which include special warning sounds to indicate danger. Since they are small in stature and, therefore, easily preyed upon, they have developed a variety of calls to indicate the presence of danger.

Their calls have been divided into six different groups including “peeps,” “twitters,” “chuck-chucks,” “cackles,” “pulsed calls,” and “noisy calls.” “Chuck-chucks” are the most commonly used vocalizations and are used when descending rapidly from trees, during mother-child interactions, and during sexual activities.

Scent marking is another method in communication—they urinate on their hands and feet and rub it all over their bodies as a way to leave a scent trail for others to be able to follow them through the forest.

Reproduction and Family

These polygamous primates typically only have one or two males in a troop who copulate frequently with multiple females.

Sexual maturation is reached among females at 3.5 years and menopause occurs in their mid-teens. For males, sexual maturity occurs at around 2.5 years of age. The seasonally “fattened” males receive the most female attention during breeding season, which lasts typically from early August to early October.

Females are often chased, pinned down, and inspected to determine their sexual receptivity levels, which is done by examining their genitals.

Their 145-day long gestation period results in a synchronized birthing schedule among members in a troop to decrease the changes of predation. The first 5-10 weeks of an infant’s life is spent being protected and carried around by the mother, as they are primarily responsible for infant care. After 8 to 10 months, they are matured enough to take care of their own survival.

Ecological Role

Like all fruit-eating primates, black-headed squirrel monkeys aid in replanting the forest as they drop partially eaten fruit or excrete seeds in their travels. In addition, they aid in controlling the insect population by consuming them. They also play a role in the food chain by serving as prey for certain carnivores. 

Conservation Status and Threats

The International Union for Conservation of Nature lists the black-headed squirrel monkeys as Endangered (IUCN, 2020) appearing on the IUCN’s Red List of Threatened Species. Its entire range is confined to one location within an area of occupancy of 335 square miles (870 km²), which is split into three geographically isolated subpopulations with no demographic or genetic exchange: Mamirauá Sustainable Development Reserve, Capucho and Tarará islands. Although this protected area is well managed and free of hunting, it is susceptible to selective logging, especially along the main stream of the Solimões River. The most imminent threat to this habitat and the squirrel monkeys is climate change, which is predicted to radically disrupt the annual precipitation cycle for the entire specialized flooded forest environment that is the unique habitat for this species.

Conservation Efforts

The black-headed squirrel monkey is listed on Convention on International Trade in Endangered Species (CITES) Appendix II.

The entire range of the black-headed squirrel monkey is found within the Mamirauá State Sustainable Development Reserve, located in the heart of the Amazonian region of Brazil. This reserve is unique because it was the first conservation in Brazil to integrate the involvement of traditional communities to help teach how to hunt and fish sustainably without causing harm to the creatures within the habitat.  


Written by Nina Shangari, June 2018. Conservation status updated April 2021.