Life span: 20 years
Total population: 3500 (S. o. oerstedti and S. o. citrinellus), other species unknown
Regions: Costa Rica, Panama, Venezuela, Colombia, French Guiana, Guyana, Suriname, Bolivia, Peru, Brazil
Gestation: 4.8 months (145 days)
Height: 269 to 318 mm (M & F)
Weight: .649 to 1.25 kg (M), .649 to .898 kg (F)
Species: S. boliviensis, S. oerstedti, S. sciureus, S. ustus, S. vanzolinii
Subspecies: S. b. boliviensis, S. b. peruviensis, S. o. citrinellus, S. o. oerstedti, S. s. albigena, S. s. cassiquiarensis, S. s. macrodon, S. s. sciureus
Other names: S. boliviensis: black-headed squirrel
monkey or Bolivian squirrel monkey; macaco de cheiro (Spanish); boliviansk dödskalleapa,
boliviansk ekorrapa, or svarthövdad dödskalleapa (Swedish); S.
oerstedti: S. oerstedtii or S. oerstedii;
black crowned Central American squirrel monkey, Central American squirrel monkey,
or red-backed squirrel monkey; panamavsaimiri (Finnish); saimiri à dos
roux, singe écureuil à dos rouge, or singe écureuil à dos
roux (French); geel doodshoofdaapje (Dutch); gelbes totenkopfäffchen (German);
testina di morto (Italian); barizo dorsirrojo, mono ardilla, mono tití,
or saimiri dorsirrojo (Spanish); nordlig dödskalleapa, rödryggad dödskalleapa,
or rödryggad ekorrapa (Swedish); S. sciureus: common
squirrel monkey or South American squirrel monkey; saimiri ecureuil (French);
macaco de cheiro (Spanish); ekorrapa gråhövdad dödskalleapa,
gråhövdad ekorrapa (Swedish); S. ustus: bare-eared
squirrel monkey or golden-backed squirrel monkey; barörad dödskalleapa,
nakenörad dödskalleapa, or nakenörad ekorrapa (Swedish); S.
black squirrel monkey, black-headed squirrel monkey, or blackish squirrel monkey;
mörk dödskalleapa (Swedish)
Photo: Luiz Claudio Marigo
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 (Groves 2001). 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 (Groves 2001).
Even though there are slight morphological differences among squirrel
monkey species, all have the same general facial and body colorations
and are easily distinguished as part of the genus. Squirrel monkeys
have white masks of fur around their eyes and dark brown or black
coloration around the mouth and chin. Species are separated by the
shape of the arch of white fur over their eyes, and are either
characterized as having a "roman" or "gothic" arch (Rowe 1996; Groves
2001). The species in the Saimiri sciureus group have a
"gothic" arch in which the white fur is dramatically high and the darker
fur on their heads forms a deep "V" shape between their eyes. S.
boliviensis and S. vanzolinii are categorized in the
Saimiri boliviensis group and have a "roman" arch of fur which
is more rounded than the "gothic" type and does not extend as far up
onto the forehead. The gray or black fur on their head makes a very
shallow "V" pattern between their eyes (Groves 2001).
Saimiri boliviensis peruviensis
Photo: Rosie Bolen
S. oerstedti subspecies are predominantly orange to
golden-orange over their backs, hands, feet, and forearms while the
crown fur is blackish in females or blackish-brown in males. Their hips
and shoulders are grayish-brown and the base of the tail is also this
color but is tipped in black (Rowe 1996). They have tufts of fur on
their ears and their heads appear very round. S. o.
citrinellus are sexually
dichromatic with males having gray crown fur and females exhibiting
black crowns (Groves 2001). The average height for both male and female
S. oerstedti is 270 mm (10.6 in), but males weigh more than
females. Average weights in males range from 750 to 950 g (1.65 to 2.1
lb), depending on the time of year, while females weigh between 600 and
790 g (1.32 to 1.74 lb) (Groves 1996; Boinski et al. 2002). The common
squirrel monkey, S. sciureus subspecies, has brownish-gray
crowns and have less red-orange pelage than S. oerstedti. They
are mainly greenish-gray to auburn but S. s. sciureus and
S. c. macrodon have orange or yellow hands, feet, and forearms.
Differing in the coloration of the forearms and hands from the other
subspecies, S. s. albigena exhibits grayish-brown coloration
with a very pale orange tinge (Groves 2001). Average weights of S.
sciureus range between 554 and 1150 g (1.22 to 2.53 lb) for males
and 651 to 1250 g (1.43 to 2.76 lb) for females, with the males
measuring only slightly longer than the females at 318 mm (12.5 in)
compared to 316 mm (12.4 in) (Rowe 1996). The bare-eared squirrel
monkey, S. ustus, stands apart from the other species because
of its lack of ear tufts. It is also orange or yellowish on its
forearms, hands, and feet with brownish-gray on the head (Groves 2001).
Saimiri oerstedti oerstedti
Photo: Sue Boinski
In addition to having a "roman" arch pattern over their eyes, S.
boliviensis and S. vanzolinii have remarkably thin tails
compared to members of the Saimiri sciureus group (Groves
2001). S. boliviensis females have gray bodies while males
have black bodies. Both sexes have yellow fur on the forearms, hands,
and feet (Rowe 1996). Males and females are similar heights, 310 mm
(12.2 in) on average, but males are heavier than females, weighing
between 963 and 1088 g (2.12 to 2.4 lb), depending on the season while
females weigh between 700 and 900 g (1.54 to 1.98) (Rowe 1996). The
black squirrel monkey, S. vanzolinii, gets its name from the
black band from the crown to the tail. The feet, hands, and forearms
are a light yellow (Groves 2001). Height ranges from 275 to 295 mm
(10.8 to 11.6 in) in females and 278 to 320 mm (10.9 to 12.6 in) in
males, while females weigh significantly less than males, 650 g (1.43
lb) and 950 g (2.09 lb), respectively (Rowe 1996).
Male and female squirrel monkeys are seasonally sexually dimorphic. Male squirrel
monkeys have widely fluctuating weights throughout the year and gain
weight during the two months prior to the breeding season, taking on a
"fatted" appearance from water and fat stored between the
muscle and skin on their head, shoulders, upper arms, and ribs. During
this period of growth they can gain up to 20% of their body weight
and the larger they appear, the more attractive they are to females
(Boinski 1987a; Kinzey 1997).
Squirrel monkeys are quadrupedal
and move through the forest preferentially traveling on branches between
one and two centimeters in diameter (.394 and .787 in). They rarely come to the
ground and when they do, it is to forage or play and they are rarely seen
leaping horizontal distances greater than two meters (6.56 ft) (Boinski et al.
19981998; Kauffman pers. comm.).
CURRENT RANGE MAPS (IUCN REDLIST):Saimiri boliviensis
| Saimiri oerstedti
| Saimiri sciureus
| Saimiri ustus
| Saimiri vanzolinii
Squirrel monkeys are found widely throughout Central and South America.
S. boliviensis is distributed throughout Brazil, Bolivia,
Colombia, Peru, and Venezuela. S. b. boliviensis is found in
Brazil, Peru, and Bolivia while S. b. peruviensis is found in
only in Amazonian Peru (Groves 2001; Gold 2004). The Central American
squirrel monkey, S. oerstedti, is found in Costa Rica (both
subspecies) and Panama (S. o. oerstedti only) and is completely
geographically separated from the other species of squirrel monkeys
found in South America (Groves 2001). Once long thought to be separated
from the other South American species because of introduction into
Central America by early humans, molecular data prove that S.
oerstedti is, in fact, endemic to this region (Cropp &
Boinski 2000). S. sciureus is distributed across several
countries: Brazil, Colombia, French Guiana, Guyana, Suriname, and
Venezuela. The most restricted in range of the squirrel monkeys is
S. vanzolinii which can be found only on the left bank of Lago
Mamirauá and at the mouth of the Rio Japura in Brazil (Groves
2001). S. ustus ranges in Brazil south of the Amazon (Groves
Since 1981, Sue Boinski has studied squirrel monkeys in the wild,
focusing her long-term research on S. o. oerstedti in Costa
Rica at Corcovado and Manual Antonio National Parks. She has also done
comparative research on S. b. boliviensis at Manu National Park
in Peru (Kinzey 1997). More recently, Boinski has continued working
with squirrel monkeys in a long-term study of S. sciureus in
the Central Suriname Nature Preserve in Raleighvallen, Suriname. Most of
the literature from field work comes from studies done at one of these
four parks, but captive research has supplemented information about wild
squirrel monkeys. Saimiri are the second-most used primates in
captive research after rhesus macaques (Macaca mulatta) and have been
studied widely across a variety of institutions and by a number of
researchers (Kinzey 1997).
Squirrel monkeys are found primarily in tropical lowland rainforest
throughout the Amazon basin from Paraguay to Guyana and in Costa Rica
and Panama. Squirrel monkeys are habitat generalists and have
few restrictive requirements in regard to forest type compared to other
neotropical primate; they can survive in a myriad of habitat types,
including disturbed and edge forests (Kinzey 1997; Kauffman pers. comm.). Across their range,
squirrel monkeys are found in similar habitat types ranging from
undisturbed tropical and evergreen primary forests, selectively logged
tropical forests, secondary growth
tropical forests, and disturbed or edge forests (Boinski 1987b; Rowe
1996; Kinzey 1997; Boinski 1999; Boinski et al. 2002). There is marked
seasonality in most of these ecosystems, with the dry season lasting from
approximately January to March and the rainy season from April to
December with coinciding periods of fruit and flower abundance (Boinski
Though they are geographically widespread, squirrel monkeys exhibit very
little difference in ecological behavior because the habitats in which
they are found are quite similar (Boinski 1999; Boinski et al. 2002).
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 (Boinski & Timm 1985; Kinzey 1997;
Boinski 1999). 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 (Boinski 1988; Janson & Boinski 1992).
Saimiri preferentially ingest small, soft, berry-like fruits
less than one centimeter in diameter found in the lower and middle
canopies of the forest (Janson & Boinski 1992; Kinzey 1997). The
small vertebrates consumed include bats, which they systematically
search for in large stands of trees, small birds, and bird eggs (Janson
& Boinski 1992). During the year, the period of greatest food
abundance is between April and June (Boinski 1988).
Photo: Luiz Claudio Marigo
Differences in distribution of available resources across study sites
and species leads to different levels of intragroup feeding competition.
In Suriname, very small, dense patches of fruit characterize the
feeding sites of S. sciureus while in Costa Rica, S.
oerstedti forages in fruit patches which are larger but which have
few ripe fruits available in each patch. S. boliviensis in
Peru forages in the largest fruit patches with the highest densities of fruit
in any squirrel monkey study site (Boinski 1999). In Costa Rica, where
each fruit tree is depleted quickly by foraging squirrel monkeys, there
is little within-group competition for resources because individuals
simply move on to another patch after such a short time. In Peru,
though, where there is a higher density of available fruit, within-group
competition at feeding sites is high as group members have incentive to
protect the particular area of the patch in which they are foraging.
Among common squirrel monkeys, S. sciureus, within-group
feeding competition is intense because fruit is found in small, dense
patches easily monopolized by one monkey. The incentive to protect this
patch is high and the result is direct feeding competition between
members of the group. Between-group aggression is also seen in S.
sciureus but not in S. oerstedti or S.
boliviensis (Boinski et al. 2002).
Home range sizes and population densities are available for S.
oerstedti at Corcovado National Park and for S.
boliviensis at Manu National Park in Peru. At Corcovado, squirrel
monkeys have home range sizes of about 2 km² (.77
mi²) and the population density is 36 individuals per
km² (22 per mi²) compared to Manu where they have home range sizes about 2.5 to 5 km² (.97 to 1.93 mi²) and
live in densities of 60 per km² (37 per mi²) (Mitchell et al.
1991). S. sciureus have home ranges between 2.5 and 3
km² (.97 and 1.16 mi²) and live in much lower
densities than other species with only 13 individuals per km² (8
per mi²) (Boinski et al. 2002). Squirrel monkeys exhibit similar daily
activity patterns, regardless of species, and spend more than half of
their day traveling and foraging for insects, while about 11% of
their day is spent feeding on fruit and nectar, another 10% of
their day is spent resting, and the remainder of their day is spent
doing miscellaneous activities such as social behavior and self-grooming
(Mitchell et al. 1991).
Their small body size makes squirrel monkeys susceptible to a variety of
predators across their range including raptors, snakes, and felids (Mitchell et al. 1991).
Raptors are responsible for the highest number of observed predations on
squirrel monkeys (Boinski et al. 2002). One predator avoidance pattern
seen in squirrel monkeys in Peru is prolonged associations with other
primate species. Saimiri and Cebus 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 Cebus, which serves to alert group members of
potential predators (Sussman 2000). Squirrel monkeys may also benefit
from maintaining proximity to Cebus in terms of gaining access
to previously unexploited resources. Cebus use similar fruit
sources and small ranges and squirrel monkeys can exploit
Cebus' knowledge of these ranges to utilize new fruit patches
(Kinzey 1997; Sussman 2000).
Content last modified: March 16, 2006
Written by Kristina Cawthon Lang. Reviewed by Laurie Kauffman.
Cite this page as:
Cawthon Lang KA. 2006 March 16. Primate Factsheets: Squirrel monkey (Saimiri) Taxonomy, Morphology, & Ecology . <http://pin.primate.wisc.edu/factsheets/entry/squirrel_monkey/>. Accessed 2015 January 30.