Black squirrel monkeys (Saimiri vanzolinii) are native to the tropical rainforests of South America; however, the geographic range of this species is the smallest of all South American primates. These animals live only in northern Brazil in a small section of Amazonian floodplain at the convergence of the Amazon and Japura rivers. Their range reaches as far west as the Paraná Auatí-Paraná and is situated in a corner of Brazil’s Mamirauá Sustainable Development Reserve. Excluding swamp areas scattered throughout the Reserve, the range of black squirrel monkeys is no greater than 533 km^2. (Bristol Zoo Gardens, 2006; Guynup, 2002; Schwindt, 2005)
There are no recognized differences between the habitat preferences, behaviors, ecology, and social habits of black squirrel monkeys and their close relatives, common squirrel monkeys (Saimiri sciureus), which are the most intensively studied species of Saimiri. Squirrel monkeys occur mainly in tropical lowland rainforests, at elevations between 23 and 80 m. They are habitat generalists and can survive in various forest habitats. Squirrel monkeys can be found in undisturbed tropical forests, edge forests, primary evergreen forests, as well as logged tropical forests. (Lang, 2006; MacDonald, 1987; Rhines, 2000)
Black squirrel monkeys grow to an average length of 31.75 cm, with the tail adding an additional 40.64 cm on average to the total length. The short and thick coat is black to greyish in color, with yellow or reddish legs. The skin around the lips and nostrils is black and hairless. Most squirrel monkeys are white around the eyes and neck. The underparts are shades of yellow and white. They weigh between 0.68 and 1.13 kg. When resting, the tail often curls over one shoulder. Like other primates, squirrel monkeys have sharp nails. Squirrel monkeys are sexually dimorphic, with males being larger than females. (Lang, 2006; MacDonald, 1987; Rhines, 2000)
Data on mating in most species within the genus Saimiri are lacking. However, S. sciureus has been fairly well studied. It is reported to breed polygynandrously, and other members of the genus are expected to be similar. Members of the genus Saimiri typically form large mixed-sex groups. Males fatten and become reproductively acting only during the mating season. During this time, they compete for access to females. Physical altercations may result in serious wounds. Subordinate and subadult males may be marginalized in these competitions, preventing them from access to mates. (Nowak, 1999; Robinson and Janson, 1987)
Females do not apparently descriminate between mates, and may accept matings with multiple males. Females do not have external signs of estrus, although estrus females may produce chemicals in their urine to which males respond. In S. sciureus, females are reported to show passive tolerance of males, and may even initiate some mating mounts. Males may also advertize their breeding condition to females through chemicals in their urine. (Robinson and Janson, 1987)
Squirrel monkeys breed seasonally, mating from September to November. Estrus in Saimiri is short-lived, lasting only 12 to 36 hours. If pregnancy does not occur, the estrus cycle will last betweeen 6 and 25 days. Gestation takes between 140 and 170 days, and the birth season coincides with the greatest period of rainfall and food availability. Females typically give birth to a single infant between February and April.
Females reach sexual maturity at about 2.5 years of age, but males may mature later, becoming reproductive between 2.5 and 4 years of age. (Bristol Zoo Gardens, 2006; Campbell, et al., 2006; Lang, 2006; Oakland Zoo, 2003; Rhines, 2000; Robinson and Janson, 1987)
Withing Saimiri, newborns are reported to weigh about 100 g. For the first few weeks of life, a young squirrel monkey clings to its mother's back. The duration of lactation is probably around 6 months. These animals grow quickly, and are independent by the age of one year. A female may produce another offspring after a year. (Nowak, 1999; Robinson and Janson, 1987)
Male squirrel monkeys generally do not help in raising young. Mothers nurse their infants for approximately 6 months. During this time the mother provides the infant with grooming, socialization, and teaches it valuable life skills. (Bristol Zoo Gardens, 2006; Rhines, 2000; Schwindt, 2005)
Black squirrel monkeys are diurnal and arboreal. They spend more than half of the day foraging for insects. Another 25% of their day is divided between searching for fruit and nectar and resting. They spend the remainder of their day socializing and self-grooming.
Squirrel monkeys live in groups composed of up to 300 individuals. Smaller subgroups form during the non-mating season based on common characteristics such as sex, age, and family roles. During mating season, the females of the group are the dominant sex. Female squirrel monkeys with no infants of their own may form relationships with other mothers’ young, acquiring what Rhines (2000) refers to as an "aunt-like" role.
There is a dominance hierarchy among males but the basis for that hierarchy is unknown. There are few clashes between groups regarding territories, as squirrel monkeys are inclined to remain within their own home ranges to avoid disputes with other groups. Different groups can be found together when searching for food, but this is only temporary and will end when the search for food is complete.
Black squirrel monkeys travel quickly through the forest, running on branches in the upper canopy. Saimiri oerstedii in Panama has been reported to travel as far as 4.2 km in a single day. Saimiri sciureus has been reported to travel between 0.7 and 2.3 km per day. It is not known how far S. vanzolinii groups travel each day, but their activity probably falls within the range of variation for the genus. Their daily activities typically occur around some source of water. (Campbell, et al., 2006; Lima and Ferrari, 2003; MacDonald, 1987; Nowak, 1999; Rhines, 2000; Rylands, et al., 2003)
Black squirrel monkeys are generally quiet, but produce a shrill cry when alarmed. Females make a “chucking” sound to communicate with other members of the group while feeding in dense areas of the forest. They have also been seen spreading urine on their hands and feet, which emits a strong scent for wandering individuals to find their way back to the group (Bristol Zoo). The urine may also provide information on the reproductive status of an individual. As in all primates, grooming and tactile communication is common. In addition, facial expressions and body postures are likely to be of some importance. (Boinski and Cropp, 1999; Lang, 2006; Oakland Zoo, 2003; Boinski and Cropp, 1999; Lang, 2006; Oakland Zoo, 2003; Robinson and Janson, 1987)
Black squirrel monkeys are omnivorous. Whether they favor fruit or insects in their diet depends upon the abundance of each during various seasons. If both resources are scarce, black squirrel monkeys will extend their diet to include small vertebrates, flowers, seeds, leaves, and nectar. Squirrel monkeys favor small, berry-like fruits growing in the forest’s lower and middle canopies. They prefer stationary insects resting on plants to those they must catch while in motion. To catch insects, squirrel monkeys search leaf surfaces and uncurl dead plants, preferring grasshoppers and caterpillars to other insects. Squirrel monkeys will consume small vertebrates such as bats and small birds. They are also known to eat eggs.
According to Lima and Ferrari’s (2003) research monitoring the feeding behavior of the closely related species, S. sciureus in Brazil, their diet consists of 55.1% reproductive plant parts and 44.9% arthropods. These authors suggest that squirrel monkeys prefer insects but consume fruits as well.
Because they are relatively small in size, black squirrel monkeys are vulnerable to many predators. Their most common predators are raptors, large snakes, and felids. Black squirrel monkeys my have some protection from predation provided by their group structure; their social nature means that more animals are on alert for potential danger and groups may be able to mob some predators. (Campbell, et al., 2006; Lang, 2006; Campbell, et al., 2006; Lang, 2006)
The role of black squirrel monkeys in their ecosystems has not been fully described. It is likely that they disperse some seeds through their frugivory. They may limit populations of some insects and small vertebrates. In addition, they provide food for a variety of predators, although the significance of this species of monkey in the diet of any predatory species is not known.
Black squirrel monkeys are sold as pets and used in various types of research, especially biomedical research, because they are small and easy to handle. While international trade in squirrel monkeys is regulated, these animals are locally sold as food and pets. (MacDonald, 1987)
Black squirrel monkeys are easily maintained in captivity. Threats to this species include habitat destruction, capture for the pet trade or medicinal purposes, and illegal hunting. The continued existence of black squirrel monkeys is threatened because of their extremely localized range. Habitat loss due to logging or other practices severely threatens S. vanzolinii. Hybridization with other species of Saimiri may also be a risk, as other species in the genus occupy the same habitat. (Lang, 2006; Rhines, 2000; Rylands, et al., 2003)
Tanya Dewey (editor), Animal Diversity Web.
Nancy Shefferly (editor), Animal Diversity Web.
Abby Williams (author), University of Notre Dame, Karen Francl (editor, instructor), Radford University.
living in the southern part of the New World. In other words, Central and South America.
uses sound to communicate
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
Referring to an animal that lives in trees; tree-climbing.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
union of egg and spermatozoan
A substance that provides both nutrients and energy to a living thing.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
an animal that mainly eats all kinds of things, including plants and animals
the business of buying and selling animals for people to keep in their homes as pets.
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
places a food item in a special place to be eaten later. Also called "hoarding"
uses touch to communicate
Living on the ground.
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
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MacDonald, D. 1987. Encyclopedia of Mammals. Oxford: Equinox.
Nowak, R. 1999. Walker's Mammals of the World, Sixth Edition. Cambridge and London: The Johns Hopkins University Press.
Oakland Zoo, 2003. "Animals A-Z: Squirrel Monkey" (On-line). Oakland Zoo. Accessed March 25, 2006 at http://www.oaklandzoo.org/atoz/azsqmky.html.
Rhines, C. 2000. "Animal Diversity Web" (On-line). Accessed March 05, 2006 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Saimiri_sciureus.html.
Robinson, J., C. Janson. 1987. Capuchins, Squirrel Monkeys, and Atelines: Socioecological Convergence with Old World Primates. Pp. 69-82 in B Smuts, D Cheney, R Seyfarth, R Wrangham, T Struhsaker, eds. Primate Societies. Chicago: The University of Chicago Press.
Rylands, A., M. Bampi, G. de Fonseca, S. Mendes, M. Marcelino. 2003. "The IUCN Red List of Threatened Species" (On-line). Accessed March 25, 2006 at http://www.iucnredlist.org/search/details.php/19839/all.
Schwindt, D. 2005. "NYU Information Technology Services" (On-line). The Distribution of the Black Squirrel Monkey. Accessed March 20, 2006 at http://www.nyu.edu/its/pubs/connect/archives/01spring/SchwindtMonkey.html.