Squirrel monkeys are any of the species of monkeys that belong to the taxonomic genus Saimiri. The species and subspecies are distinguished mostly from fur coloring and shape, rather then behavior differences. They live in Central and South America and have similar habitats even though the range is very widespread. They eat insects and fruit, and best time of year for these particular food groups is between April and June. During this time of year there is little competition for food between the monkeys and other organisms.
Males and females have a 2 month breeding period. The males over this period have a time of fattening to become larger. They do this because they look more attractive to females the larger they are. No matter what, usually the monkeys have several partners, in which it is normal to have a single infant. Their mothers raise them to maturity, unlike the fathers who have nothing to do with the infants after birth.
The Squirrel monkey has a wide range of fur colors on its body. The head usually ranges in color from a grayish color to black. The monkey's forearms, hands, and front feet are reddish or yellow most of the time and their shoulders and hind feet are grayish as well. They have a bi-colored tail with a black tip and also have black lips which are nearly hairless. The eyes,ears, throat and side of the neck all tend to have a white coloring. Also, this primates thighs are shorter then their lower legs to attain more jumping power.
The squirrel monkey is an omnivore which means they eat everything. Even though they can digest alot, a lack of vitamin C in the diet can cause scurvy in squirrel monkeys. They have been used in studies of this disease to better learn about why this happens and how it can be prevented. Without vitamin C,these animals can develop very serious diseases. These animals can digest everything from berries to frogs and mollusks, but without the vitamin C they can be infected with this disease which is deadly to them.
These primates were one of the very first to be a model for human atherosclerosis and are still studied to gain knowledge about blood pressure and cardiovascular disease. This primate's heart rate is fast and has a fast metabolism.
Squirrel monkeys operate in large groups led by a dominant male. The dominant male only mates with receptive females and does not try to control the members. However, all males and females have several partners. After birth, females will have a single infant which is always close by their mom, unlike the father which has no role in parenting the infant.The squirrel monkey's breeding season is in September. Females tend to prefer males that advance most over the mating season due to testosterone. They choose the enlarged males because they tend to be older and are better at detecting predators that may harm them and their possible infant. The males do not fight over females, and do not try and force copulation, which is often unseen in the animal world. From these observations, it looks as if the female chooses a mate and is not chosen.
This gestation period last 6 months and all offspring are born in a week in February and March,resulting usually in a single infant. Of all the infants born,only 50% survive past the first 6 months, a good percent due to predatory birds. Females reach sexual maturity at about 2 and a half years old, and males at about 4-5 years of age, at which they both stop being dependent on their mothers. After females reach maturity, they usually leave their group unlike the males who normally stay with their group. Once at full maturity, males can choose to leave the group to try and contest with males in other groups to improve their chances of reproduction. Then, once they find mates the process of mating starts all over again back at the infant stage. Females are receptive to males from other groups, except that monkeys from that group will give him heavy competition in which he is unlikely to beat. 
Squirrel monkeys are geographically widespread, their habitats are so similar that the behavior of the monkeys are almost identical to the others. The monkeys like to eat insects and fruit. They rarely chase insects that are in the air, instead they hunt them while they are stationary on the leaves. The best time for food is between April and June. This is a good time of year because when there is a large amount of food and resources, the less competition between other monkeys and organisms there is.
These monkeys live in the canopies of Central and South America. Most species have ranges in the Amazon,but the species S. oerstedii is found in Costa Rica and Panama. The habitats of the primate ranges from undisturbed forests, selectively logged tropical and evergreen forests, and secondary growth forests. The seasons in these habitats are a dry season from January to March, and a rainy season from April to December.
Even though these monkeys dwell in the canopy, because of their small bodies, they fall prey to many other animals such as birds, raptors, snakes, and felids. To avoid these predators, the squirrel monkey associates with the other species. Saimiri and Cebus have been seen in Peru mixing into groups with each other. It benefits Saimiri because of the Cebus alarm system which alerts all the monkeys of any potential predators. Also by sticking together,these 2 species get to use each others resources which also benefits both species since those resources of the other species would have not been accessible to the other.
There are differences between the squirrel monkey species, yet they are very slight. Saimiri sciureus have a gothic arch in which the white fur is high up and the dark hair on their heads forms a V shape.
S. boliviensis and S. vanzolinii have a roman arch of their fur which creates a more rounded shape then the gothic of the other group. Compared to Saimiri sciureus group, they also have very thin tails. S.boliviensis males have black bodies while the females have grey, but both have yellow arms, hands, and feet. Males and females have a height of 12.2 inches on average, but the males are heavier weighing between 2.1 to 2.4 pounds. S.vanzolinii have yellow arms, feet, and hands and a black band around their tail. This subspecies gets around 10-12 inches tall, and in common with other subspecies, the males weigh significantly more then the females.
S. oerstedti subspecies are orange on their hands, feet, and back and have blackish crown fur on their forearms. The hips and shoulders and brownish-gray and the bottom of their tail is black with brownish-gray making up the rest of the tail. They have heads which appear to be very round and have hair on their ears. Males weigh more then females, even though they tend to be the same height of 10.6 inches.
Male and female squirrel monkeys are seasonally sexually dimorphic. Males have diverse weights throughout the year and gain weight 2 months before their breeding season, in which the males have a 'fatted' looking state all over their bodies. During this period of fattening they can gain 20% of their body weight. This is good for the males because the larger they look, the more attractive they appear to females.
- Squirrel monkey by Wikipedia, accessed Feb.18,2010.
- Squirrel Monkey by Kristina Cawthon Lang, WPRC, March 16,2006.
- Monkey Anatomy by Phoenix Zoo, 2006.
- Squirrel monkey internal by Alan G.Brady, National Academy of Sciences.