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
Predators of S. boliviensis include harpy eagles (Harpia harpyja) and humans. Eagles are avoided by staying in large groups and remaining vigilant.
Known Predators:
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
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.
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
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 )
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
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
Bolivian squirrel monkeys have no adverse effects on humans.
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
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
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)
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
Link to Primate Info Net's webpage on this genus. Provides comprehensive information about taxonomy, morphology, ecology, behavior, and conservation.
The black-capped squirrel monkey (Saimiri boliviensis) is a species of New-World monkey native to the upper Amazon basin in Bolivia, western Brazil and eastern Peru.[3][4] They weigh between 365 and 1135 grams and measure, from the head to the base of the tail, between 225 and 370mm.[5] Black-capped squirrel monkeys are primarily tree-dwelling and are found in both native and plantation forests as well as some farmed areas near running water.[4] Their diet is omnivorous and mostly consists of flowers, fruit, leaves, nuts, seeds, insects, arachnids, eggs and small vertebrates.[6] They mostly live in female-dominated troops of around 40 to 75 monkeys, with males having been observed to disperse to live in all-male troops after reaching sexual maturation.[7] Their current conservation status according to the IUCN is 'Least Concern'.[8] The species belongs to the genus Saimiri and has two subspecies, S. b. boliviensis (the Bolivian squirrel monkey) and S. b. peruviensis (the Peruvian squirrel monkey).[9]
The black-capped squirrel monkey displays sexual dimorphism, with males normally weighing between 550 and 1135 grams and females weighing between 365 and 750 grams.[5][6] Infants typically weigh between 80 and 140 grams when they are born.[10] Adults of the species measure in length (from the head to the base of the tail) between 250 and 370mm for males and 225 and 295mm for females. The coat of the monkey is short, soft and dense, and the majority of the fur covering the back of the monkey is a grey to olive-brown hue, while the undersides are typically white, yellow or ochre.[6] The head is characteristically black with white arches over the eyes. The tail is the same colour as the body with a black tufted tip and is not prehensile; it usually measures around 350 to 425mm.[4]
Physically, the black-capped squirrel monkey is very similar to a number of other species of squirrel monkey, but is distinguishable from other species by a number of features. The most noticeable of these are the dark black cap and the white ‘Roman type’ arch pattern over the monkey's eyes, which is more narrow and rounded than the ‘Gothic type’ arch pattern over the eyes of the other species.[11] The tail of the ‘Roman type’ species is also narrower than that of the ‘Gothic type’.[9]
Saimiri boliviensis is thought to have diverged from the Saimiri genus approximately 1.5 million years ago.[12][13] It has been hypothesised that this diversification occurred due to environmental changes in the Pleistocene period which allowed for thicker vegetation to appear in the Amazonian rainforest.[13]
Several different fossils have been linked to the genus Saimiri through examinations of their dental and cranial morphology, including the Early Miocene fossil Dolichocebus which was discovered in Gaiman, Argentina and dated to around 20.5 million years ago, and the Middle Miocene fossil of the genus Neosaimiri discovered in La Venta, Colombia, which has been dated to between 12.1 and 12.5 million years ago.[13]
Originally all squirrel monkeys were considered to be of the same species;[14] they were first divided into two different ‘types’ - ‘Roman’ and ‘Gothic’ - in Paul D. Maclean's article ‘Mirror Display in the Squirrel Monkey, Saimiri sciureus’, published in 1964.[15] Many different opinions on the taxonomic classification of Saimiri boliviensis as a separate species have been published,[14] however various studies conducted by several researchers have concluded that Saimiri boliviensis is one of at most seven different species of Saimiri.[16][14] Based on the geographical distribution and the morphological and behavioural characteristics of the specimens studied, Hershkovitz proposed the existence of Saimiri boliviensis as a distinct species with two sub-species, Saimiri boliviensis boliviensis and Saimiri boliviensis peruviensis.[9][17] Based on cranial measurements and coat colouring, Thorington proposed Saimiri sciureus boliviensis as a sub-species of Saimiri sciureus.[2][17] Another prominent report published in 1993 supports Thorington's classification,[16] however after further investigation into the genetic characteristics of the monkey a more recently published report concludes that Hershkovitz's description is the most accurate.[18] The dispute over the taxonomic and genetic classification of the black-capped squirrel monkey has become increasingly relevant with regards to their use in biomedical research, due to the fact that hybridisation may have an effect on the reproductive capabilities of the monkey,[19] and has the potential to cause a differentiation in its susceptibility to certain pathogens and infections.[20]
Alternative or previously proposed taxonomic names include:[2]
Saimiri displaying the characteristic ‘Roman arch’ facial pattern of the black-capped squirrel monkey have been documented throughout most of Bolivia, northern Peru, and between the Jurua and Purus Rivers in Brazil.[2] They are found in lowland tropical rainforests near water in densely forested and swampy regions.[21][10] They are predominantly arboreal, and while they utilise all levels of the forests they have been observed to keep mostly to the lower canopies for the purposes of travel and foraging[10] It has been proposed that matrilineal troops of Saimiri boliviensis are formed due to an abundance of fruit and insects present in their habitat, which is not present in the habitats of other species of the Saimiri genus.[21]
Saimiri boliviensis are mostly arboreal but will occasionally also be found on the forest floor. They are diurnal and have been observed to be most active during the early to mid-morning, before resting for one or two hours in the afternoon, followed by another period of activity from the early afternoon to evening.[4]
The black-capped squirrel monkey is found in female dominated troops of around 45 to 75 monkeys, unlike its relative the Common squirrel monkey which habitually lives in male dominated troops of around 15 to 50.[12] Similar to most other species of monkeys, female Saimiri boliviensis will remain in the troop into which they are born, while males are more likely to be excluded by more dominant females.[21] When they reach sexual maturity, male Black-capped squirrel monkeys will disperse from their natal troop into smaller all-male groups, and will eventually join a larger mixed-sex troop, often together with other males from the all-male group.[7] Black-capped squirrel monkey troops display high levels of aggression between females.[12] Female monkeys will often compete with other female members of the troop to determine access to resources,[7] however it has been observed that despite heavy competition for food they still prefer to live in large groups in order to reduce the likelihood of predation.[21]
A Black-capped squirrel monkey will typically reach sexual maturation at around 3 years of age for females and 5 years of age for males.[4][6] The yearly reproductive cycle of mature Saimiri has been observed by several researchers to be affected by a number of environmental factors, including the cycles of rainfall and levels of illumination in their habitat. The mating season coincides with the dry season, and will typically result in a single infant being born to each mother.[8] It has been suggested that adult female monkeys are more receptive to environmental cues for the mating season to begin, and the response in males is in part attributed to behavioural and scent cues from the females.[10] During the mating season, males of the species will gain a large amount of subcutaneous upper body fat, leading to what is known as a ‘fatted’ appearance. It has also been observed that the testosterone levels of monkeys of the Bolivian and Peruvian species are noticeably higher during the mating season than those of other species of male Saimiri from Guayana.[22] Males will become more irritable and aggressive, fight more frequently for the purpose of achieving dominance within the troop, and engage in genital display towards less dominant males.[10] It has been observed in both natural and laboratory settings that the hierarchy of the troop may change up to as often as three times in a month, and this will often result in highly aggressive fights which may lead to the complete exclusion of younger adult males from the troop.[10] The scent and behavioural cues of a female monkey assist a male in his judgement of whether or not she will be receptive to his approach and attempt at mating with her. If she is not receptive, the female, sometimes with the aid of other nearby females, will usually chase the male away.[10] Consorting and copulation between a male and female monkey may last between one minute and over an hour depending on the presence of other monkeys and the environment in which it takes place. The gestation period of the monkey has been estimated to last between 160 and 170 days.[10] During the first week following its birth, an infant monkey will cling to its mother's back and will seldom move or be attended to by the mother unless it is in some way in need of assistance.[10]
Squirrel monkeys have been found to be some of the most vocal primates, with a large range of different types of calls documented throughout their lifespan.[4] Commonly used sounds include ‘chucks’,[23] a variety of purrs and squawks elicited during the birthing and mating seasons, chirps and peeps used for alarm or attention, as well as aggressive screaming and ‘barking’.[4] Infant Black-capped squirrel monkeys tend to vocally communicate much more than adults.[23] The most common form of infant communication is a number of different ‘peeps’, which begin to occur most frequently at around 2 months of age when the infant starts to spend more time away from its mother.[23] After maturation, the most commonly used call for adult females is a variety of ‘chucks’, used to maintain contact in dense vegetation where visual identification is not possible.[24]
Black-capped squirrel monkeys are omnivorous. A typical squirrel monkey diet includes fruits, insects, eggs, small vertebrates, arachnids, leaves, flowers, nuts, seeds, and rarely fungi;[4][6][25] however it has been observed that they prefer insects to fruit.[10] Mature Saimiri spend most of the day foraging. They will begin foraging at around 60 to 40 minutes before sunrise and will spend the first part of the day actively feeding on fruits and any insects they are able to hunt while foraging for fruit.[10] They will then adopt more sedate feeding behaviours and spend the rest of the day resting and hunting for more insects. Often, when food is not scarce, they will stop and rest for an hour or two in the middle of the day when it is too hot to continue.[10] When fruits are scarce, squirrel monkeys have been reported to consume Ascopolyporus, a fungus that is parasitic on scale insects which are parasitic to local bamboo species. Researchers formulate that this is done as an alternative food source during dry seasons.[25]
Black-capped squirrel monkeys are mostly found in trees and will often leap 1–2 metres between branches. They are capable of moving swiftly through dense vegetation at a four-legged walk or run with diagonal sequence footfalls (wherein the hind leg on one side will touch down followed by the foreleg of the opposite side).[26] They will occasionally adopt a stationary bipedal stance at ground level while foraging. The monkey's tail is usually used for balance, or by infants to secure them to their mother's tail or abdomen.[10]
The black-capped squirrel monkey population has been listed as being of ‘Least Concern’ by the IUCN, despite population numbers being in a general state of decline.[8] It has been determined that the black-capped squirrel monkey is adapts easily to changes or potential threats to its environment, and is not subject to high levels of hunting by humans.[8] According to the IUCN, the main threats to the habitat of the monkey are agricultural and aquacultural uses of their habitat, and the use of the monkey's biological resources for purposes such as hunting, trapping, logging and wood harvesting.[8]
The black-capped squirrel monkey (Saimiri boliviensis) is a species of New-World monkey native to the upper Amazon basin in Bolivia, western Brazil and eastern Peru. They weigh between 365 and 1135 grams and measure, from the head to the base of the tail, between 225 and 370mm. Black-capped squirrel monkeys are primarily tree-dwelling and are found in both native and plantation forests as well as some farmed areas near running water. Their diet is omnivorous and mostly consists of flowers, fruit, leaves, nuts, seeds, insects, arachnids, eggs and small vertebrates. They mostly live in female-dominated troops of around 40 to 75 monkeys, with males having been observed to disperse to live in all-male troops after reaching sexual maturation. Their current conservation status according to the IUCN is 'Least Concern'. The species belongs to the genus Saimiri and has two subspecies, S. b. boliviensis (the Bolivian squirrel monkey) and S. b. peruviensis (the Peruvian squirrel monkey).
