Monkey, Squirrel


Saimiri sciureus


Adult length: 12.5 in.; tail length: approximately 16 in.; appearance and color: slender, lithe build, with a short grayish coat, bright yellow legs and white masks of fur around their eyes and dark brown or black coloration around the mouth and chin; non-prehensile tail often curls over one shoulder when resting; dentition: 36 teeth, and their teeth are sexually dimorphic - males have large upper canines.

Family

Cebidae

Order

Primata

Class

Mammalia

Range

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.

Habitat

Tropical forests at middle canopy, but will occasionally come to the ground or go up into the high canopy.

Life Expectancy

Sexual Maturity

Females: 2.5 years; males: 4 years

Diet

In the wild, they eat berry-like fruit, leaves, insects, tree frogs and small invertebrates; in the Zoo, they are fed a scientifically developed, commercially available primate diet, assorted fruits, vegetables, starches and insects.

Status

IUCN – Least Concern; CITES – Appendix II

Behaviors

Squirrel monkeys are insectivores-frugivores, consuming insects and fruit in their diet, depending on seasonal abundance of each resource, and supplementing their diets with small vertebrates, nectar, flowers, buds, seeds, leaves, and gum. Squirrel monkeys rarely go after insects that are in motion and prefer to capture stationary insects on plant surfaces. They hunt for insects on the surface of live leaves or by unfolding leaf curls of dead foliage and prefer caterpillars and grasshoppers over other insects. Saimiri preferentially ingest small, soft, berry-like fruits less than one centimeter in diameter found in the lower and middle canopies of the forest. The small vertebrates consumed include bats, which they systematically search for in large stands of trees, small birds, and bird eggs. They spend 75-80% of their day foraging. During the year, the period of greatest food abundance is between April and June. The common squirrel monkey is polygynous with a multi-male, multi-female group structure. Most social interactions 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 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 common squirrel monkeys. Adult males are generally socially inactive during the birth season and spend their time traveling and foraging at a distance from the group. During the breeding season, 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. Non-receptive 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. Mating occurs between September and November, with births occurring from February through 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. 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 age, infants can find food. 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 common squirrel monkey 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 them 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 different 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 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. All males emigrate from their natal group and some females may as well, although the females are more often philopatric (remaining in birth group). 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.

Adaptions

Their small body size makes squirrel monkeys susceptible to a variety of predators across their range including raptors, snakes, and felids. Raptors are responsible for the highest number of observed predations on squirrel monkeys. One predator avoidance pattern seen in squirrel monkeys in Peru is prolonged associations with other primate species. Squirrel monkeys and capuchin monkeys are seen forming mixed-species groups and associating for many days. These interactions are peaceable and squirrel monkeys benefit from the extensive alarm calling system of capuchins, which serves to alert group members of potential predators. Squirrel monkeys may also benefit in terms of gaining access to previously unexploited resources. Capuchins use similar fruit sources and small ranges, and squirrel monkeys can exploit their knowledge of these ranges to utilize new fruit patches.

Special Interests

Color vision in squirrel monkeys has been extensively studied as a stand-in for human ailments. In humans, two genes for color vision are found on the X chromosome. Typically, one gene (OPN1LW) produces a pigment that is most sensitive to the 564 nm wavelength, while the other gene (OPN1MW) produces pigment most sensitive to 534 nm. In squirrel monkeys, there is only one gene on the X chromosome but it exists in three varieties: one is most sensitive to 538 nm, one to 551 nm and one to 561 nm. Since males have only one X chromosome, they are dichromatic (a form of color-blindness in which only two light wavelengths are distinguished rather than the usual three) although with different sensitivities. Females, on the other hand, have two X chromosomes, so some of them can have copies of two different alleles. The three alleles seem to be equally common, leading to one-third of females being dichromatic while two-thirds are trichromatic (the condition of possessing three independent channels for conveying color information, derived from the three different cone types). Recently, gene therapy has given the human OPN1LW gene to adult male squirrel monkeys, producing behavior consistent with trichromatic color vision. Until recently, there were only two species of squirrel monkeys, a South American species, S. sciureus and a Central American one, S. oerstedti, but with genetic tools increasingly available, the genus has been reclassified into five species based on genetic, physical, and behavioral characteristics. Squirrel monkeys are now divided into two groups, the Saimiri sciureus group, containing S. oerstedti subspecies, S. sciureus subspecies, and S. ustus and the Saimiri boliviensis group, containing S. boliviensis subspecies and S. vanzolinii. Most of the literature and information available on squirrel monkeys does not make these newer distinctions and focuses on the traditional taxonomy with only two species.

Folklore

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. Habitat destruction, illegal hunting, and capture for the pet trade or medical research all pose threats and problems to the squirrel monkeys. This species is listed as Least Concern, given its relatively wide range, adaptability to some degree of disturbed forest, and apparent lack of major threats. Additionally, given its small size, it is not generally hunted. However, populations undoubtedly are declining in some areas due to forest destruction and fragmentation.

Conservation

Jacksonville Zoo History

Our earliest records for this species show it as part of our animal collection from 1972 to 1985. Squirrel Monkeys returned in 2004 and we have a very successful ongoing breeding program with this species.

Exhibit

Play Park Exhibit Area