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)
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).
Communication Channels: visual ; tactile ; acoustic ; chemical
Other Communication Modes: pheromones
Perception Channels: visual ; tactile ; acoustic ; chemical
This species has not currently been evaluated by international conservation databases. They rely on intact rainforests, so are vulnerable to deforestation.
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: least concern
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).
Positive Impacts: pet trade ; food ; body parts are source of valuable material; research and education
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.
Ecosystem Impact: disperses seeds
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).
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).
Animal Foods: birds; mammals; amphibians; reptiles; eggs; insects; terrestrial non-insect arthropods; mollusks
Plant Foods: leaves; seeds, grains, and nuts; fruit; flowers; sap or other plant fluids
Primary Diet: omnivore
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.
Biogeographic Regions: neotropical (Native )
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).
Range elevation: Sea Level to 1500 m.
Habitat Regions: tropical ; terrestrial
Terrestrial Biomes: rainforest
Other Habitat Features: riparian
Bolivian squirrel monkeys have lived up to 30 years in captivity.
Range lifespan
Status: captivity: 30 (high) years.
Typical lifespan
Status: captivity: 15 to 20 years.
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).
Range mass: 365 to 1135 g.
Range length: 225 to 370 mm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger; sexes colored or patterned differently
Predators of S. boliviensis include harpy eagles (Harpia harpyja) and humans. Eagles are avoided by staying in large groups and remaining vigilant.
Known Predators:
Within a troop of Bolivian squirrel monkeys, mature males live in a subgroup, generally separate from a female/young subgroup (Hinde, 1983). This level of segregation between males and females is unique among Bolivian squirrel monkeys. Theories as to what causes this separation include social dynamics between the males, and female initiated active exclusion (Gibson,Kuehl, and Ruiz, 2005). During the mating season, males, who have a well-developed dominance hierarchy, will interact and mate with the females. The dominance hierarchy in males is based on testosterone levels and copulatory frequency (Gibson,Kuehl, and Ruiz, 2005) as well as fierce fighting (Nowak, 2000). Among males, the more dominant male is allowed to interact with the females. Females will often mate with several males during their short mating season. When a male wishes to mate with a female, he will use an aggressive behavior while making his penis erect. This behavior is also used when approaching an inferior male (Bourne, 1971). When the female becomes submissive, the male mounts her from behind. This mounting behavior has been observed in infants and juveniles who apparently develop the behavior without penetration before maturity (Schrier, 1977). During mating season, males have been known to gain considerable amounts of weight. This "fattening" helps the males by increasing their sperm production. Saimiri boliviensis are polygynandrous creatures, meaning that both males and females in the troop may mate with multiple partners in a given breeding season. Males that do mate with multiple mates are usually the more dominant males (Ruiz et al., 2005). Following the mating season, males and females once again segregate into different groups (Hinde, 1983). Squirrel monkeys also display cooperative breeding behavior, meaning that the mother has help from other females in raising her young (Carpenter, 1973).
Also called “aunting”, cooperative breeding is where helpers provide help in raising young that is not their own. In Bolivian squirrel monkey troops, females will act as “aunts” to the infant of another female. Aunting behavior includes dorsal carriage (carrying the infant on their back), retrieval, and cleaning. “Aunts” can be any female in the group but primarily consist of females who the mother spent a lot of time with prior to birthing, females who the mother previously acted as an “aunt” to, or previously birthed females. As many as nine different subjects have been observed interacting with a given infant in the first week of life. This “aunting” behavior is unique to squirrel monkeys and is thought to create, maintain, and extend group cohesiveness over long periods of time (Carpenter, 1973).
Mating System: polygynandrous (promiscuous) ; cooperative breeder
The breeding season for S. boliviensis is restricted to three months in length with estrus times averaging 7-8 days in length (Gibson,Kuehl, and Ruiz, 2005). Unique among squirrel monkeys is their highly synchronized mating seasons, where every female will come into estrus at approximately the same time. Heavy scent marking by females during the mating season may result in this level of synchronisity. The coordination of fertility among females of the troop may be influenced by these sexual pheromones (Ankel-Simons, 2000). In each breeding season a female will have one offspring (Gibson,Kuehl, and Ruiz, 2005). The gestation period is between 152 and 172 days and weaning occurs between four and six months old (Napier and Napier, 1967). Females reach sexual maturity generally around two and a half to three years of age. Males, on the other hand, will usually leave the female/young subgroup of the troop at two and a half to three years of age. From here the adolescent males will form their own subgroup in the troop, consisting of immature males that cannot compete with the older males for dominance. At around five years of age, the males will join the mature male subgroup and begin to compete for dominance (Gibson,Kuehl, and Ruiz, 2005).
Breeding interval: Bolivian squirrel monkeys breed once yearly.
Breeding season: Breeding is restricted to 3 months of the year, synchronized by females in a group.
Average number of offspring: 1.
Range gestation period: 152 to 172 days.
Range weaning age: 4 to 6 months.
Average time to independence: 1 years.
Range age at sexual or reproductive maturity (female): 2.5 to 3 years.
Average age at sexual or reproductive maturity (male): 5 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous
Parental investment by Bolivian squirrel monkeys is taken on entirely by the females. Upon birth of the infant, the mother protects her offspring and provides entirely for it. Responsibilities include dorsal carriage, cleaning, retrieval, and nursing. Mothers are protective of their offspring and don't let them wander far.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female); post-independence association with parents; extended period of juvenile learning; inherits maternal/paternal territory
