Squirrel monkey

How to read a taxoboxSquirrel monkeys[1]
Common Squirrel Monkey, Saimiri sciureus
Common Squirrel Monkey, Saimiri sciureus
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Family: Cebidae
Subfamily: Saimiriinae
Miller, 1912 (1900)
Genus: Saimiri
Voigt, 1831
Type species
Simia sciureus
Linnaeus, 1758
Species

Saimiri oerstedii
Saimiri sciureus
Saimiri ustus
Saimiri boliviensis
Saimiri vanzolini

Squirrel monkey is the common name for the small, tropical, arboreal New World monkeys comprising the genus Saimiri of the primate family Cebidae, characterized by a small white face with black mouth and nose, relatively large eyes and ears, a long nonprehensile tail, and short fur, which typically is greenish or olive on the shoulders but yellowish orange on the back and extremities. Saimiri is the only genus in the subfamily Saimirinae.

Squirrel monkeys are gregarious and live together in groups in the tropical forests of Central and South America. Their range extends from Costa Rica through central Brazil and Bolivia.

Squirrel monkeys are important to food chains in their ecosystems, feeding on insects, fruit, and other food sources (bats, birds, nectar, leaves, etc.), while themselves being prey for raptors (falcons, eagles), snakes, and felids. The common squirrel monkey (S. sciureus) is captured for the pet trade and for medical research (Rhines 2000). While it is not endangered, three squirrel monkey species are in danger of extinction. S. o. oerstedti is listed as "endangered," S. o. citrinellus is listed as "critically endangered," and S. vanzolinii is listed as "Vulnerable."

In addition to these values, squirrel monkeys add immeasurably to the enjoyment of nature for human beings, whether seen in the wild moving from tree to tree or observed in zoos.

Contents

Overview

Squirrel monkeys are New World monkeys. New World monkeys are one of three major informal groups of the biological order Primates, the other two groups being (1) prosimians and (2) monkeys and apes of the Old World. Together, the New World monkeys and the Old World monkeys and apes are considered to be "higher primates," or simians (infraorder Similformes), while the prosimians (such as lemurs) are considered to be the "lower primates." The term monkey thus refers to any simian that is not an ape or any primate that is neither an ape or a prosimian. In reality, monkeys are not a single coherent group and therefore do not have any particular traits that they all share. The New World monkeys are found in Mexico, Central America, and South America, and the Old World monkeys are located in Africa, central to southern Asia, Japan, and India.

There are four families of New World monkeys: Cebidae, Aotidae, Pitheciidae, and Atelidae (Groves 2001). The four families are ranked together as the Platyrrhini clade. All New World monkeys differ slightly from Old World monkeys in many aspects, but the most prominent of which is the nose. This is the feature used most commonly to distinguish between the two groups. The scientific name for New World monkey, Platyrrhini, means "flat nosed," therefore the noses are flatter, with side facing nostrils, compared to the narrow noses of the Old World monkey.

Most New World monkeys have long, often prehensile tails (adapted for grasping or holding). However, squirrel monkeys have "nonprehensile tails." Many New World monkeys are small, arboreal (live in trees), and nocturnal (active at night). Unlike most Old World monkeys, many New World monkeys form monogamous pairs, and show substantial paternal care of young.

Squirrel monkeys belong to the Cebidae family with the marmosets, tamarins, and capuchin monkeys.

Description

Squirrel monkeys grow to 25 to 35 centimeters (9.8 to 13.8 inches), plus a 35 to 42 centimeter (13.8 to 15.5 inches) tail. They weigh 750 to 1100 grams (1.7 to 2.4 pounds). Remarkably, the brain mass to body mass ratio for squirrel monkeys is 1:17, which gives them the largest brain, proportionately, of all the primates. Humans have a 1:35 ratio.

There are slight morphological differences among species of squirrel monkeys, but the same basic facial and body colorations are shared (Cawthon Lang 2006). All species have white fur around eyes, and dark coloration around the mouth and chin. The fur of squirrel monkeys is short and close, typically colored olive, greenish gray, or grayish brown at the shoulders and yellowish orange, orange, golden-orange, or with a pale orange tinge on the back and extremities (Cawthon Lang 2006). The tails are tipped in black. Their throats and ears are white. The upper part of their head is hairy. This black and white face gives them their German name, "skull monkeys."

All species and subspecies except the bare-eared squirrel monkey (S. ustus) have tufts on their ears.

Female squirrel monkeys have a pseudo-penis that they use to display dominance over smaller monkeys, much like the way the male squirrel monkeys display their dominance.

Behavior, diet, and reproduction

Like most of their New World monkey relatives, squirrel monkeys are diurnal and arboreal. They rarely come to the ground, although they may do so to forage or play (Cawthon Lang 2006). They move from branch to branch by leaping, with their shorter thighs relative to lower legs allowing more jumping force (Oakland Zoo 2007). Unlike the other New World monkeys, their tail is not used for climbing, but as a kind of "balancing pole" and also as a tool. Their movements in the branches are extremely speedy.

Squirrel monkeys live together in multi-male/multi-female groups with up to 500 members. These large groups can, however, occasionally break into smaller troops. They have a number of vocal calls, including warning sounds to protect themselves from large falcons and eagles, which are a natural threat to them. Feeding in large groups also makes their numbers too great to be chased from the trees by larger monkeys (Oakland Zoo 2007). Glandular secretions in their fur and especially the tail provide a scent to mark territory and leave a trail for others in the troop to follow, while the odor also turning away some predators (Oakland Zoo 2007).

Squirrel monkeys are omnivores, eating primarily fruits and insects. Occasionally, they also eat nuts, buds, leaves, eggs, and small vertebrates. Small vertebrates consumed include bats and small birds (Cawthon Lang 2006). Preference among insects appears to be caterpillars and grasshoppers (Cawthon Lang 2006). Overall, the various species exhibit similar dietary habits (Cawthon Lang 2006).

Given the small body size of squirrel monkeys, their predators include snakes, raptors, and felids, with raptors responsible for most observed predations (Cawthon Lang 2006). In Peru, an association of squirrel monkeys and Cebus has been observed, with squirrel monkeys appearing to benefit from the alarm calling system of Cebus (Cawthon Lang 2006).

The mating of the squirrel monkeys is subject to seasonal influences. Females give birth to young during the rainy season, after a 150- to 170-day gestation. The mothers exclusively care for the young. Saimiri oerstedti are weaned by four months-of-age, while S. boliviensis are not fully weaned until 18 months old. Female squirrel monkeys reach sexual maturity at age three years, while males take until age five. They live to about 15 years old in the wild, about 20 years in captivity.

Classification

Currently, five species of squirrel monkey are recognized, placed into two groups. The Saimii sciureus group includes S. oerstedii, S. sciureus, and S. ustus, along with various subspecies. The Saimii boliviensis group contains S. boliviensis and two subspecies, and S. vanzolinii.

This is in contrast with the traditional taxonomy for genus Saimiri, which recognized only two species, S. sciureus and S. oerstedti (Cawthon Lang 2006). However, the genus was reclassified into five species and various subspecies based on genetic, behavioral, and physical characteristics (Cawthon Lang 2006).

  • Genus Saimiri
    • S. sciureus group
      • Central American Squirrel Monkey, Saimiri oerstedii
        Black-crowned Central American Squirrel Monkey, Saimiri oerstedii oerstedii
        Grey-crowned Central American Squirrel Monkey, Saimiri oerstedii citrinellus
      • Common Squirrel Monkey, Saimiri sciureus
        Saimiri sciureus sciureus
        Saimiri sciureus albigena
        Humboldt's Squirrel Monkey, Saimiri sciureus cassiquiarensis
        Ecuadorian Squirrel Monkey, Saimiri sciureus macrodon
      • Bare-eared Squirrel Monkey, Saimiri ustus
    • S. boliviensis group
      • Black-capped Squirrel Monkey, Saimiri boliviensis
        Bolivian Squirrel Monkey, Saimiri boliviensis boliviensis
        Peruvian Squirrel Monkey, Saimiri boliviensis peruviensis
      • Black Squirrel Monkey, Saimiri vanzolini

Notes

  1. C. Groves, "Order Primates," "Order Monotremata," (and select other orders). Page(s) 138-139 in D. E. Wilson and D. M. Reeder, eds., Mammal Species of the World, 3rd edition, Johns Hopkins University Press (2005). ISBN 0801882214.

References

  • Groves, C. 2005. Order Primates. In D. E. Wilson and D. M. Reeder, eds., Mammal Species of the World, 3rd edition. Johns Hopkins University Press. ISBN 0801882214.
  • Rhines, C. (2000). Saimiri sciureus. Animal Diversity Web. Retrieved June 7, 2008.


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