Saimiri boliviensis
Bolivian squirrel monkey

Saimiri boliviensis, Bolivian squirrel monkeys, can be found in the tropical rain forests of South America. They are found from the Andes in the east, north to the Caribbean Sea, and south and east into Brazil. (Ankel-Simons, 2000)

Bolivian squirrel monkeys are most commonly found in gallery forests, but will also inhabit forest edges (Ankel-Simons, 2000). Within these tropical rain forests, Saimiri boliviensis are typically arboreal, residing in the canopy among the small branches. However, they will occasionally leave the canopy to the shrub layer or the forest floor to scavenge (Napier and Napier, 1967; Nowak, 2000). They occur at elevations from sea level to 1500 meters (Napier and Napier, 1967). (Ankel-Simons, 2000; Napier and Napier, 1967; Nowak, 2000)

Squirrel monkeys (Saimiri) are all fairly similar in appearance. The head is elongated and egg-shaped (Napier and Napier, 1967). It has been suggested that this characteristic cranial morphology is a compromise between a small facial skeleton and a relatively large braincase (Ankel-Simons, 2000). The fur of Bolivian squirrel monkeys is dense and short, and is generally a yellowish tan color, mottled with black hair tips (Ankel-Simons, 2000). The fur on the undersides of the limbs is yellow, white, or orange (Napier and Napier, 1967). Males and females are very similar in appearance, with sexual dimorphism occurring in size and color of crown fur (gray in males and black in females). The sizes of male Bolivian squirrel monkeys range in length, weight, and tail length, from 250-370mm, 550-1135g, and 370-465mm respectively. Females are smaller than males, from 225-295mm in length, weighing 365-750g, and having tail lengths of 370-445mm (Chiarelli, 1972). The face has white areas on the cheeks and around the eyes that appear “mask-like” (Ankel-Simons, 2000). One key identifying feature of S. boliviensis that differs from other squirrel monkeys is the arched eyebrows (Gibson, Kuehl, and Ruiz, 2005). The snout of S. boliviensis is similar to other squirrel monkeys. It is short and blunt in shape and dark in color. The ears are white and tufted and are large in comparison to the monkey’s head. The tail , which has a black tip, is almost twice the length of the body but is not prehensile. However, the tail is not prehensile. They have pseudoopposable thumbs (Ankel-Simons, 2000). (Ankel-Simons, 2000; Chiarelli, 1972; Gibson, Kuehl, and Ruiz, 2005; Napier and Napier, 1967)

Bolivian squirrel monkeys have lived up to 30 years in captivity.

Saimiri boliviensis are diurnal and live in social groups ranging from 10 to 550 individuals (Nowak, 2000) with an average size of 40-50 individuals (Ankel-Simons, 2000). They are very social creatures which establish hierarchies of dominance. (Ankel-Simons, 2000; Nowak, 2000)

Males establish their dominance through fierce fighting and assert their dominance through urine-washing and forced subjugation of an inferior. Urine-washing is a behavior by which the individual urinates on its hands, feet, and body, thus ensuring that wherever it travels it will leave its trace. Through penile display, males assert their dominance over subservient males. In this behavior, the dominant male will display its penis to the other male, often urinating on him (Nowak, 2000). (Nowak, 2000)

Along with the hierarchical structure of dominance among individuals of a troop, Saimiri boliviensis is one of the few primate species, outside of humans, who exhibit a wide range of play behavior. Play is most common between mother and offspring and between two immature individuals. However, adults also play with other adults outside of the mother/offspring relationship. This is a behavior that is rarely seen in nature. (Smith, 1978)

Another unique aspect of Bolivian squirrel monkey social behavior is that the amount of social interactions between individuals correlates to the type, quantity, and dispersion of available food. When it is more difficult to find food, social interaction is reduced. (Hinde, 1983)

Home Range

The home range of a troop of Bolivian squirrel monkeys varies greatly, often dependent on the size of the troop. The average movement of S. boliviensis between 0.6 and 1.1 kilometers per day. This could roughly be translated into the size of a territory. However, individuals have been observed with a nomadic range of up to three square kilometers. Bolivian squirrel monkeys are not territorial. (Nowak, 2000)

Saimiri boliviensis is one of the most vocal squirrel monkeys. There are 26 identifiable calls, consisting of chirps and peeps (used when alarmed), squawks and purrs (used during mating and birthing seasons), barks of aggression, and screams of pain (Nowak, 2000). Bolivian squirrel monkeys also communicates with other individuals using chemical signaling. Examples of this include urine-washing (Nowak, 2000) and release of sexual pheromones by females during mating season (Ankel-Simons, 2000). Concerning perception, S. boliviensis has been shown to be polymorphic for cone pigment and color vision, meaning that, like humans, they can see in color (Ankel-Simons, 2000). (Ankel-Simons, 2000; Nowak, 2000)

The diet of S. boliviensis consists primarily of insects and fruits. Other foods eaten include berries, nuts, flowers, seeds, leaves, arachnids, and small vertebrates such as bats, birds, and eggs (Ankel-Simons, 2000). (Ankel-Simons, 2000)

Saimiri boliviensis prefers to forage on terminal branches. Often, they will forage in large groups, possibly enhancing their ability to disturb insects and increase capture rates (Rodman and Cant, 1984). (Rodman and Cant, 1984)

Predators of S. boliviensis include harpy eagles (Harpia harpyja) and humans. Eagles are avoided by staying in large groups and remaining vigilant. ("Rainforest Alliance", 2005)

Having a primary diet of insects and fruits, S. boliviensis would play several important roles in the ecosystem. First, by eating insects, the insect population is kept in check. Second, by consuming fruit, Bolivian squirrel monkeys act as an agent for seed dispersal. Many seeds cannot germinate or disperse properly without the help of animal digestion.

Bolivian squirrel monkeys have no adverse effects on humans.

Bolivian squirrel monkeys are sometimes captured for food or for the pet trade. There was once a large trade in squirrel monkeys in the United States for both biomedical research and as entertainment (zoos and pet markets). Between 1968 and 1972, more than 173,000 squirrel monkeys were used for medical research. Regulations were then established that reduced trade in squirrel monkeys for non-research reasons (Nowak, 2000). (Nowak, 2000)

This species has not currently been evaluated by international conservation databases. They rely on intact rainforests, so are vulnerable to deforestation.

Bolivian squirrel monkeys have the ability to move by bipedal walking. This is generally only used by a mother when carrying an infant that doesn't have the ability to grasp the dorsal fur of its mother. Also, squirrel monkeys use their tails as an accessory, both to balance and to use as a third leg when bipedally walking (Napier and Napier, 1967) (Napier and Napier, 1967)