Animal Diversity Web

Ge­o­graphic Range

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)

• Biogeographic Regions
• neotropical
  • native

Habi­tat

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)

• Habitat Regions
• tropical
• terrestrial

• Terrestrial Biomes
• rainforest

• Other Habitat Features
• riparian

• Range elevation

  Sea Level to 1500 m

  to 4921.26 ft

Phys­i­cal De­scrip­tion

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, et al., 2005; Napier and Napier, 1967)

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry

• Sexual Dimorphism
• male larger
• sexes colored or patterned differently

• Range mass

  365 to 1135 g

  12.86 to 40.00 oz

• Range length

  225 to 370 mm

  8.86 to 14.57 in

Re­pro­duc­tion

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). (Bourne, 1971; Car­pen­ter, 1973; Gib­son, et al., 2005; Hinde, 1983; Nowak, 2000; Schrier, 1977)

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). (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). (Ankel-Si­mons, 2000; Gib­son, et al., 2005; Napier and Napier, 1967)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
• viviparous

• 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

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. (Car­pen­ter, 1973)

• 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

Lifes­pan/Longevity

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

Be­hav­ior

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)

• Key Behaviors
• arboreal
• scansorial
• diurnal
• motile
• sedentary
• social
• dominance hierarchies

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)

Com­mu­ni­ca­tion and Per­cep­tion

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)

• Communication Channels
• visual
• tactile
• acoustic
• chemical

• Other Communication Modes
• pheromones

• Perception Channels
• visual
• tactile
• acoustic
• chemical

Food Habits

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)

• Primary Diet
• omnivore

• 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

Pre­da­tion

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)

• Known Predators

  • harpy eagles (Harpia harpyja)
  • humans (Homo sapiens)

Ecosys­tem Roles

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

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

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)

• Positive Impacts
• pet trade
• food
• body parts are source of valuable material
• research and education

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

Bo­li­vian squir­rel mon­keys have no ad­verse ef­fects on hu­mans.

Con­ser­va­tion Sta­tus

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

• IUCN Red List

  Least Concern
  More information

• IUCN Red List

  Least Concern
  More information

• US Federal List

  No special status

• CITES

  No special status

Other Com­ments

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)

Con­trib­u­tors

Tanya Dewey (ed­i­tor), An­i­mal Di­ver­sity Web.

Lev­ent Sipahi (au­thor), Kala­ma­zoo Col­lege, Ann Fraser (ed­i­tor, in­struc­tor), Kala­ma­zoo Col­lege.

Ref­er­ences

2005. "Rain­for­est Al­liance" (On-line). Ac­cessed No­vem­ber 23, 2005 at http://​www.​rainforest-alliance.​org/​resources/​forest-facts/​species-profiles/​squirrelmonkey.​html.

Ankel-Si­mons, F. 2000. Pri­mate Anatomy: An In­tro­duc­tion, Sec­ond Edi­tion. San Diego: Aca­d­e­mic Press.

Bourne, G. 1971. The Ape Peo­ple. New York: Aca­d­e­mic Press.

Car­pen­ter, C. 1973. Be­hav­ioral Reg­u­la­tors of Be­hav­ior in Pri­mates. Lewis­burg, PA: Buck­nell Uni­ver­sity Press.

Chiarelli, A. 1972. Tax­o­nomic Atlas of Liv­ing Pri­mates. Lon­don: Aca­d­e­mic Press.

Gib­son, S., T. Kuehl, J. Ruiz. 2005. "Squir­rel Mon­key Breed­ing and Re­search Re­source" (On-line). Ac­cessed No­vem­ber 23, 2005 at http://​www.​smbrr.​org/​.

Hinde, R. 1983. Pri­mate So­cial Re­la­tion­ships: An In­te­grated Ap­proach. Ox­ford: Black­well Sci­ence Ltd..

Napier, J., P. Napier. 1967. A hand­book of liv­ing pri­mates. Lon­don: Aca­d­e­mic Press.

Nowak, R. 2000. Walker's Pri­mates of the World. Bal­ti­more: John Hop­kins.

Rod­man, P., J. Cant. 1984. Adap­ta­tions for For­ag­ing in Non­hu­man Pri­mates: Con­tri­bu­tions to an Or­gan­is­mal Bi­ol­ogy of Prosimi­ans, Mon­keys, and Apes. New York: Co­lum­bia Uni­ver­sity Press.

Schrier, A. 1977. Be­hav­ioral Pri­ma­tol­ogy. Hills­dale, NJ: Lawrence Erl­baum As­so­ci­ates, Inc..

Smith, E. 1978. So­cial Play in Pri­mates. New York: Aca­d­e­mic Press.