Saimiri sciureus sciureus is a wide-ranging subspecies in the north-eastern and eastern Amazon. Distribution, according to Hershkovitz (1984), extends through the Guianas, Amapá and the Brazilian Amazon east of the Rios Deminí and Negro north of the Rio Amazonas, and east of the Rio Xingú south of the Rio Amazonas, Guyana. Silva Jr. (unpublished) places it east of the rios Tapajós and Juruena to extending east to upper reaches of the Rio Teles Pires, a little north and then east, south of the Serra od Cahimobo, across the middle Xingu, the Araguaia and Tocantins to the Rio Parnaiba valley in Maranhão. Hershkovitz (1984) placed its eastern limit as the Rio Pindaré in Maranhão. It also occupies a small area south of the Rio Solimões between the Rio Madeira and the Tapajós on the Ilha Tupinambarama, east to Parintins. Saimiri s. sciureus has not been recorded above 100 m above sea level.
The range of Saimiri sciureus albigena according to Hershkovitz (1984) is gallery forests of the Colombian llanos (Llanos Orientales) from the eastern slope of the Cordillera Oriental in the Departments of Arauca, Casanare and Guaviare, and the departments of Boyacá, Cundinamarca, and Meta to unknown limits eastward. It also occurs in the upper Río Magdalena, but how far it extends north in the Magdalena valley is not known (Hernández-Camacho and Cooper 1976; Defler 2003; 2004). Altitudinal range between 150 and 600 m or higher, possibly to 1,000 m.
The range of Saimiri sciureus cassiquiarensis according to Hershkovitz (1984) is the upper Amazon and Orinocean regions, in Brazil the state of Amazonas from north of the Rio Solimões and west of the Rios Demini and Negro into the Orinoco-Cassiquiare basin in Venezuela, form there west into eastern Colombia between the Ríos Apaporis and Inírida in the Departments of Vaupés, Guaviare and Guiania (Hernández-Camacho and Cooper 1976; Defler 2003; 2004). Occurrence in Venezuela was mapped by Bodini and Pérez-Hernández (1987) and Linares (1998).
Saimiri sciureus macrodon, according to Hershkovitz (1984), ranges in upper Amazon, in Brazil in the state of Amazonas between the Rios Juruá and Japurá, westward; in Colombia from the Rio Apaporis south into eastern Ecuador, throughout the Ecuadorian Amazon east pf the Andes to asltitidues of 1,200 m (Tirira 2007), and into Peru in the departments of San Martín and in Loreto, to the north bank of the Río Marañon-Amazonas. Hershkovitz (1984) indicated that the portion of the range between the Ríos Ucayali and Tapiche is occupied by both S. s. macrodon and S. boliviensis peruviensis (see also Aquino and Encarnación 1994). In Peru, it extends south as far as the ríos Amazonas and Marañón and west of the Huallaga to the Andes, south to a little beyond 8ºS. It extends south of the Rio Amazonas east of the Río Ucayali from the Rio Blanco, where it is sympatric with Saimiri boliviensis peruviensis (Aquino and Encarnación 1994). East of the Ucayali it ranges south to the west of the Serra do Divisor, but not known to reach the Río Tamaya.
Squirrel monkeys live in the tropical rainforests of South America, except in the southeastern coastal forests of Brazil.
Biogeographic Regions: neotropical (Native )
Squirrel monkeys are up to 12.5 inches long (body length), with a tail of approximately 16 inches. They have a slender, lithe build, with a short greyish coat and bright yellow legs. Their non-prehensile tail often curls over one shoulder when they are resting. They have 36 teeth, and their teeth are sexually dimorphic in that males have large upper canines.
Squirrel monkesy possess nails instead of claws, and they have been called 'small, nervous primates'. They are the smallest of the Primate family Cebidae.
Average mass: 925 g.
Average basal metabolic rate: 4.429 W.
Habitat and Ecology
Squirrel monkeys are small frugivore-insectivores. They spend 75-80% of their day foraging for insects and other small animal prey (Mittermeier and Van Roosmalen 1981; Terborgh 1983; Boinski 1988). During dry season shortages of appropriate fruiting trees they are able to depend entirely on animal prey (Janson and Boinski 1992).
Saimiri groups are multi-male and can be large, up to 100 animals (larger groups are believed to be temporary mergers of two) but most frequently are of 20-75 individuals (Baldwin and Baldwin 1981; Terborgh 1983; Mitchell et al. 1991). As emphasized by Boinski (1999a,b; 2005; Boinski et al. 2005a,b), allthough all squirrel monkeys are morphologicallly very similar, their social systems are quite distinct (summarized in Sussman 2000).
In S. sciureus, studied in Suriname by Boinski (1999a,b, 2005; Boinski et al. 2005a,b), group sizes range from 15 to 50, and both sexes form a single, linear hiearchy in the group, with most males being dominant to females. Aggression between females is uncommon, but they do not form coalitions. Males form coalitions and can aggressive to each other. Males show vigilance in defense agianst predators. The fruits they exploit typically occur in small but extremely dense patches, and there is considerable feeding competition between group members, much higher than in S. boliviensis.
Mating and births in Saimiri are highly seasonal, seldom exceeding two months in duration. Single offspring. Mating usually occurs during the dry season. In S. sciureus, birth synchrony is less pronounced and births occur only once every two years.
Saimiri boliviensis and S. sciureus frequently form interspecific associations, travelling with Cebus albifrons or Cebus apella (Terborgh 1983; Wallace et al. 2000), benefitting from the disturbance casued by the capuchin monkeys above them which flushes out insects.
Weight: Adult male 740 g, adult female more than 635 g (Jack 2007).
Squirrel monkeys prefer primary and secondary forest, gallery forest and forest edge.
They prefer the intermediate forest levels, but they can sometimes be found on the ground or in upper canopy levels.
They occupy many different types of forests.
Terrestrial Biomes: forest ; rainforest
Squirrel monkeys eat mainly fruit and some insects; they also consume some leaves and seeds. The first hour or so of the day is spent searching and collecting fruit. From then on, they look also for spiders and insects. A group spreads throughout the forest in all canopy levels to search for food.
Animal Foods: insects; terrestrial non-insect arthropods
Plant Foods: leaves; seeds, grains, and nuts; fruit
Primary Diet: herbivore (Frugivore )
Life History and Behavior
Reconciliation in captive Guyanese squirrel monkeys (Saimiri sciureus).
The tendency for agonistic interaction to increase the probability of friendly interaction between social partners has been demonstrated across a range of Old World primates. While research on such post-conflict behavior proceeds into an hypothesis-testing phase, new comparative information must accumulate to provide full phylogenetic perspective on primate social behavior. Data from New World and prosimian primates are yet extremely limited. We studied captive squirrel monkeys (Saimiri sciureus) via post-conflict (PC) and matched control (MC) observations and analyzed results using both the PC-MC and time-rule methods. Former opponents maintaining affiliative relationships soon engaged in friendly interaction following large proportions of agonistic interactions, whereas non-affiliated individuals, including virtually all male-female pairs, reconciled conflicts rarely. Close-proximity approaching and huddling contact constituted the principal modes of post-conflict amicability. Agonistic interactions of relatively high intensity were most likely to be reconciled and most likely to be reconciled via physical contact. High vulnerability of Saimiri to predation may have favored this species' strong inclination to reconcile soon after agonistic interaction. Research on free-living populations of this and other primate species is needed to illuminate similarities and differences across taxa. Am. J. Primatol. 50:159–167, 2000. © 2000 Wiley-Liss, Inc.
- Pereira, M. E., Schill, J. L. and Charles, E. P. (2000), Reconciliation in captive Guyanese squirrel monkeys (Saimiri sciureus). Am. J. Primatol., 50: 159–167. doi: 10.1002/(SICI)1098-2345(200002)50:2<159::AID-AJP6>3.0.CO;2-F
Status: wild: 21.0 years.
Status: captivity: 27.0 years.
Status: captivity: 22.7 years.
Status: captivity: 21.0 years.
Lifespan, longevity, and ageing
Within their own group, squirrel monkeys are promiscuous.
Mating System: polygynandrous (promiscuous)
Squirrel monkeys are seasonal breeders. They mate between September and November, with birth between February and April. Gestation lasts 160-170 days. The birth season is short and occurs during the time of greatest rainfall, perhaps because the wet season brings an abundance of food and water.
Males are mature at 4 years of age; females are mature at 2.5 years of age.
Breeding season: Squirrel monkeys mate between September and November
Range gestation period: 160 to 170 days.
Average age at sexual or reproductive maturity (female): 2.5 years.
Average age at sexual or reproductive maturity (male): 4 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous
Average birth mass: 107 g.
Average number of offspring: 1.
Average age at sexual or reproductive maturity (male)
Sex: male: 1826 days.
Average age at sexual or reproductive maturity (female)
Sex: female: 1003 days.
Female squirrel monkeys nurse and care for their infants until they are independent. The fathers take no part in raising young.
Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Protecting: Female)
Molecular Biology and Genetics
Statistics of barcoding coverage: Saimiri sciureus
Public Records: 7
Specimens with Barcodes: 12
Species With Barcodes: 1
Barcode data: Saimiri sciureus
There are 8 barcode sequences available from BOLD and GenBank. Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species. See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
IUCN Red List Assessment
Red List Category
Red List Criteria
- 2003Least Concern(IUCN 2003)
- 1996Lower Risk/least concern
Currently, captive squirrel monkey populations are maintained in research labs.
Threats to wild squirrel monkeys include eagles in the trees and snakes on the ground.
Squirrel monkeys are easily kept in captivity, and they were once frequently sold as pets.
Habitat destruction, illegal hunting, and capture for the pet trade or medical research all pose threats and problems to the squirrel monkeys.
IUCN Red List of Threatened Species: least concern
Klein and Klein (1975) recorded a density of 50-80 individuals/km² at La Macarena, Colombia;
Peres (1997) estimated population densities at the following várzea (white-water flooded forest) sites: Nova Empresa 73.8 individuals/km²; Barro Vermelho II 109.5 individuals/km²; Lago da Fortuna 189.8 individuals/km². They are more scarce in terra firma forests: Sobral 5.9 individuals/km²; Condor 36.1 individuals/km²; Barro Vermelho I 16.7 individuals/km²; Fortuna 23.2 individuals/km²; Vira Volta 17.7 individuals/km²; Riozinho 36.4 individuals/km².
In Colombia, Saimiri sciureus albigena occurs in a region subject to high rates of deforestation.
Saimiri sciureus sciureus
Tumucumaque National Park (3,882,376 ha)
Cabo Orange National Park (630,017 ha)
Gurupí Biological Reserve (272,379 ha)
Lago Piratuba Biological Reserve (394,223 ha)
Rio Trombetas Biological Reserve (409,578 ha)
Uatumã Biological Reserve (942,786 ha)
Jari Ecolopical Station (207,370 ha)
Terra do Meio Ecological Station (3,373,111 ha)
Niquia Ecological Station (282,803 ha)
Parc amazonien de Guyane (3,300,000 ha)
Nouragues Natural Reserve (100,000 ha) (Kessler 1998)
Kaieteur Narional Park
Brinckheuvel Nature Reserve (6,000 ha) (probable: Mittermeier and van Roosmalen 1982)
Central Suriname Nature Reserve (1,600,000 ha) (Mittermeier and van Roosmalen 1982)
Coppename Monding Nature Reserve (12,000 ha) (unconfirmed (Mittermeier and van Roosmalen 1982)
Sipaliwini Nature Reserve (100,000 ha) (Mittermeier and van Roosmalen 1982)
Brownsberg Nature Park (8,400 ha) (Mittermeier and van Roosmalen 1982)
Saimiri sciureus albigena
Cordillera de los Picachos Natural National Park (286,600 ha) (in range)
El Cocuy Natural National Park (306,000 ha) (in range?)
Serranía de la Macarena Natural National Park (630,000 ha) (in range) (or cassiquiarensis?)
Tinigua Natural National Park (201,875 ha) (in range)? (or cassiquiarensis?)
Saimiri sciureus cassiquiarensis
Pico da Neblina National Park (2,298,154 ha)
Jau National Park (2,378,410 ha)
Juamí Japurá Ecological Station (832,078 ha)
Nukak Natural National Reserve (855,000 ha) (in range)
Puinawai Natural National Reserve (1,092,500 ha) (in range)
Saimiri sciureus macrodon
Amacayacu Natural National Park (293,000 ha) (in range)
Cahuinarí Natural National Park (575,500 ha) (in range)
Serrania de Chiribiquete Natural National Park (1,280,000 ha) (in range)
Cueva de los Guacharos Natural National Park (9,000 ha) (in range)
La Paya Natural National Park (442,000 ha (in range, Polanco-Ochoa et al. 1999)
Yasuní National Park (Tirira 2007)
Cayambe-Coca Ecological Reserve (Tirira 2007)
Cofán-Bermejo Ecological Reserve (Tirira (2007)
Cuyabeno Faunal Protection Reserve (Tirira 2007)
Tamshiyacu-Tahuayo Communal Reserve (Aquino and Encanrfación 1994)
Relevance to Humans and Ecosystems
Economic Importance for Humans: Positive
Used as pets and in research.
Common squirrel monkey
The common squirrel monkey can be found primarily in the Amazon Basin, including territories in the countries of Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Peru, Suriname, Paraguay and Venezuela; a small population has been introduced to Southern Florida and many of the Caribbean Islands. A group of free-ranging individuals was spotted and photographed in 2009 at the Tijuca Forest in Rio de Janeiro - possibly the result of an illegal release or of an escape from the pet trade; by 2010, the Squirrel Monkey had begun to be considered as an invasive species in the Brazilian Atlantic rainforest, and there were concerns about its role as a predator of eggs of endangered bird species. The common squirrel monkey prefers to live in the middle canopy, but will occasionally come to the ground or go up into the high canopy. They like vegetation which provides good cover from birds of prey in the rainforest, savannah, mangroves, or marshlands.
Biology and behavior
The common squirrel monkey is considered both frugivorous and insectivorous, preferring berry-like fruit on branches. When in captivity, the squirrel monkeys are fed fruits like apples, oranges, grapes, and bananas. They also consume a variety of vegetables that include lettuce, celery, and onions. Squirrel monkeys also looks for insects, and small vertebrates, such as tree frogs. It obtains a majority of water from the foods eaten, and will also obtain water from holes in trees and puddles on the ground. When fruit is scarce, the common squirrel monkey will drink nectar.
The amount of time squirrel monkeys spend foraging depends on the type of food. When there are bigger fruits and there is an easy access, they will not spend much time foraging. Otherwise, they dedicate a considerable amount of time looking for their foods. Foraging also keeps the monkeys entertained and active. Oftentimes when they are captive, they easily become bored as the food is more easily obtained.
The common squirrel monkey is polygynous with a multi-male, multi-female group structure. Most social interactions in S. sciureus groups occur within the various age/sex classes, with the division of classes being between adult male categories, mother-infant categories, and juvenile categories. The core of the group is made up of the adult females and their young. As a result of the natural attraction each class has to the adult females, the different age/sex classes come together as one social group. Even though juveniles play and jump around an appreciable amount during phases of high activity, they usually stay close to the adult females. In terms of the males’ level of attraction to the adult females, the phase of the yearly reproductive cycle is what determines their distance from the adult females. Overall, interactions between the various age/sex classes are most frequently directed to adult females. It is important to note that the division of age/sex classes among S. sciureus is not so strictly defined because the degree of segregation between sexes can vary. That is, those subspecies which have a high degree of sexual dimorphism are sexually segregated, such that the males and females of that subspecies interact less with each other than do those of subspecies that are not very sexually dimorphic and thus sexually integrated.
The fact that reproduction is seasonal plays a major role in the social behavior of S. sciureus, where the frequency of between-sex interactions of the males and females differs between the birth season and the mating season. Adult males are generally socially inactive during the birth season and spend their time travelling and foraging at a distance from the group. On the contrary, during the mating season the adult males become fatter, excited, aggressive, and highly vocal and spend most of their time engaging in dominance interactions among themselves or following and approaching the adult females in estrus, in hopes of being able to mate with them. Males can increase their chances at copulating with receptive females by approaching them quietly. Nonreceptive females, on the other hand, respond aggressively to any male approach and will threaten and chase the males away, usually with the help of surrounding females. Overall, intersexual interaction among S. sciureus greatly increases during the mating season.
Saimiri sciureus infants develop rapidly. They become fairly independent between five to eight months of age and spend only a small percentage of the day with their mothers. Also at this range of age, the infants can find food on their own. The infants are active members of the social group, climbing, running, exploring, and frequently making contact with adult members of the group. Most adult-infant interactions are initiated by infants towards adult females who are not their mothers. Adults generally respond to the infants calmly, but some adults may respond with antagonism. Infants rank the lowest in the group.
Many other aspects of S. sciureus social behavior, such as dominance relationships, coalitions, dispersal patterns, and aggression, stem from the feeding ecology of the animals. Feeding ecology directly affects the females of the group which in turn affects the behavior of the males in the group. The feeding patches for S. sciureus are very small and dense, which makes it possible for an individual with the greatest capability of winning a fight, if one were to occur, to monopolize access to any patch. It should also be noted that within group competition among S. sciureus groups is extremely high, and between-group competition is moderate to high. Coalition formation is not as stable as would be expected among the females of the group because considering their small and dense feeding patches S. sciureus females with the greatest capability of winning a fight would benefit more if they were to form alliances to gain control of a patch and then not share the patch once in control of it.
Once sexually mature, all males emigrate from their natal group. After leaving, they may either become solitary, a peripheral of another troop, join another mixed-sex troop, or attend a tolerant troop of another monkey species. If they become a peripheral of another group, the male squirrel monkey will choose one troop and keep a certain distance away from them while still trying to follow the group. These males are the less dominant ones. A few male squirrel monkeys have been observed interacting with groups of other monkey species. Some females may leave their natal groups as well, although they tend to be more philopatric. If females do leave their natal groups, they do it after becoming sexually mature. Oftentimes they migrate before or right after a mating season. Due to this, they might end up leaving their group when they are pregnant or with their immature offspring.
Males are typically dominant to females, but females still have a high status in the group and are capable of forming coalitions against dominant males. It is very rare for males to form coalitions even if there is a group of males who keep their distance from the main group or are solitary. Several theories suggest that one of the reasons that male squirrel monkeys do not form coalitions is because the lack kinship due to emigration. Coalitions may also increase mortality risks within the group since males tend to be aggressive to each other.
Genital display among males is an important social signal in relation to group hierarchy; it is derived from sexual behavior but is used for social communication. It involves the animal spreading his thighs and having an erect penis. Dominant males display to submissive males to emphasize their higher status. The dominant males direct their action to the face of the passive males and the act can be done with the displayer leaning over the passive monkey or the displayer doing the action from a distance in a more upright position. This form of dominance interaction as well as several types of aggression increase during the mating season when males want to emphasize their rank and strength and gain more control over other males in relation to access to females. Genital displays may also define male-male alliances when the males participate in “joint genital displays”.
The common squirrel monkey is diurnal. It is usually quiet but will utter loud cries when alarmed. The common squirrel monkey uses different types of calls for specific situations. Some of their common call types include caw, bawls, and shriek. Squirrel monkeys utter caws mostly when they are trying to defend a territory. They may use bawls previous to a fight as well as after one. Shrieks are mainly heard when the monkeys are fighting for dominance. Studies have shown that the squirrel monkeys’ most common calls are determined by their genetics. Experiments have shown that the squirrel monkeys that have been isolated since infants are able to produce the same calls as those who have been exposed to the calls. There are very little variations between the frequencies of the calls of the infants who were raised differently. A squirrel monkey who was deaf since birth was also able to produce the same calls, proving that the calls come from their genes. It is arboreal but sometimes it will come down to the ground. Bands or troops can be from 12-100. Occasionally troops as large as 500 have been seen in undisturbed forests.
The common squirrel monkey is rated as "least concern" by IUCN from a conservation perspective. However, the common squirrel monkey is among many rainforest animals whose status may be harmed by deforestation. The species has also been captured extensively for the pet trade and for medical research.
Due to its inquisitive nature this species is a popular pet and it requires a large amount of space and food.
There are four subspecies of Saimiri sciureus:
- Saimiri sciureus sciureus
- Saimiri sciureus albigena
- Humboldt's squirrel monkey, Saimiri sciureus cassiquiarensis
- Ecuadorian squirrel monkey, Saimiri sciureus macrodon
In the walkthrough area of the Woburn Safari Park.
|Wikispecies has information related to: Common Squirrel Monkey|
|Wikimedia Commons has media related to Common Squirrel Monkey.|
- Boubli, J.-P., Rylands, A. B., de la Torre, S. & Stevenson, P. (2008). "Saimiri sciureus". IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature. Retrieved 19 January 2012.
- Linnæus, Carl (1758). Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I (in Latin) (10 ed.). Holmiæ: Laurentius Salvius. p. 29. Retrieved 21 November 2012.
- O Globo, 4th May 2009, Ancelmo Gois column
- O Globo, May the 25th. 2010; available at
- Sarah T. Petrucci (1993). "Observations of the Foraging Behavior of Squirrel Monkeys (Saimiri sciureus boliviensis) at the Tulsa Zoological Park". Bios 64 (3): 64–71.<http://www.jstor.org/stable/4608213>
- Mitchell C.L. (1994). "Migration alliances and coalitions among adult male South American squirrel monkeys (Saimiri sciureus)". Behaviour 130 (3-4): 169–190. doi:10.1163/156853994X00514.
- Baldwin J.D. (1968). "The social behavior of adult male squirrel monkeys (Saimiri sciureus) in a semi-natural environment". Folia Primatologica 9: 281–314. doi:10.1159/000155184. PMID 4975594.
- Anschel S., Talmage-Riggs G. (1973). "Homosexual behavior and dominance hierarchy in a group of captive female squirrel monkeys (Saimiri sciureus)". Folia Primatologica 19 (3): 61–72. doi:10.1159/000155519. PMID 4198058.
- Levine S., Lowe E.L., Mendoza S.P. (1978). "Social organization and social behavior in two subspecies of squirrel monkey (Saimiri sciureus)". Folia Primatologica 30: 126–144.
- Aruguete M.S., Mason W.A. (1996). "Effect of infants on adult social relations in the squirrel monkey (Saimiri sciureus)". Psychological Reports 79 (2): 603–611. PMID 8909087.
- Anderson C.O., Mason W.A. (1977). "Hormones and social behavior of squirrel monkeys (Saimiri sciureus): effects of endocrine status of females on behavior within heterosexual pairs". Hormones and Behavior 8 (1): 100–106. doi:10.1016/0018-506X(77)90025-3. PMID 405304.
- Boinski S., Cropp S., Henry M., Quatrone R., Selvaggi L., Sughrue K. (2002). "An expanded test of the ecological model of primate social evolution: Competitive regimes and female bonding in three species of squirrel monkeys (Saimiri oerstedii, S. boliviensis, and S. sciureus)". Behaviour 139: 227–261. doi:10.1163/156853902760102663.
- Boinski S., Mitchel C.L., van Schaik C.P. (1991). "Competitive regimes and female bonding in two species of squirrel monkeys (Saimiri oerstedi and S. sciureus)". Behavior Ecology and Sociobiology 28: 55–60.
- Sue Boinski, Erin Ehmke, Laurie Kauffman, Steven Schet, Arioene Vreedzam (2005). "Dispersal Patterns among Three Species of Squirrel Monkeys (Saimiri oerstedii, S. boliviensis and S. sciureus): II. Within-Species and Local Variation". Behaviour 142 (5): 633–677.<http://www.jstor.org/stable/4536261>
- Clark D.L, Stevens J.J, Wooley M.J. (1978). "Squirrel monkey dominance and social behavior as related to group size and group structure". Primates 19 (1): 169–177. doi:10.1007/BF02373233.
- Blitz J., Ploog D.W., Ploog F. (1963). "Studies on the social and sexual behavior of the squirrel monkey (Saimiri sciureus)". Folia Primatologica 1: 29–66. doi:10.1159/000164879.
- Kurt Hammerschmidt, Tamara Freudenstein, Uwe Jurgens (2001). "Vocal Development in Squirrel Monkeys". Behaviour 138: 1179–1204.<http://www.jstor.org/stable/4535882>