Common squirrel monkey
|Common squirrel monkey|
(Linnaeus, 1758) 
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, Hawaii 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 easy access, they will not spend much time foraging. Otherwise, they dedicate a considerable amount of time to 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 of the lack of 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 prior 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 squirrel monkeys that have been isolated since infancy are able to produce the same calls as those who have been exposed to the calls. There are very few variations between the frequencies of the calls of 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.
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