Life span: 20 years (captive)
Total population: Unknown
Regions: Panama, Colombia, Ecuador, Peru, Brazil, Paraguay, Argentina, Bolivia
Gestation: 4.5 months (133 days)
Height: 346 mm (M), 341 mm (F)
Weight: 794 to 1254 g (M), 455 to 1246 g (F)
Species: A. azarae, A. hershkovitzi, A. lemurinus, A. miconax, A. nancymaae, A. nigriceps, A. trivirgatus, A. vociferans
Subspecies: A. a. azarae, A. a. boliviensis, A. a. infulatus, A. l. brumbacki, A. l. griseimembra, A. l. lemurinus, A. l. zonalis
Other names: douroucouli or night monkey; doeroecoeli (Dutch);
douroucouli or singe de nuit (French); macaco da noite (Portuguese); cuatro ojos,
marta, marteja, mono de noche, mono nocturno, or tutamono (Spanish); mirikina,
nattapa, or negronattapa (Swedish); A. azarae: A.
azarai; Azara's night monkey; A. lemurinus: Colombian night monkey,
gray-bellied night monkey, or lemurine night monkey; A. l. brumbacki:
Brumback's night monkey; A. l. griseimembra:
grey-legged night monkey; A. hershkovitzi: Hershkovitz's
night monkey; A. miconax: Andean night monkey or Peruvian
night monkey; A. nancymaae: A. nancymai;
Nancy Ma's night monkey or Peruvian red-necked owl monkey; A. nigriceps:
black-headed night monkey or Peruvian night monkey; A. trivirgatus:
northern night monkey, northern owl monkey, or three-striped night monkey; A.
vociferans: noisy night monkey, Spix's night monkey, or Spix's owl monkey
Photo: Rosie Bolen
The Genus Aotus used to contain only one species (Aotus
trivirgatus) with ten subspecies, but in 1983, all ten subspecies
were elevated to species level and subsequent genetic work has refined
the taxonomy even more (Groves 2001). Within the genus, there are two
groups of owl monkeys, the gray-necked (lemurinus and
subspecies, hershkovitzi, trivirgatus, and
vociferans), found north of the Rio Amazonas (Amazon River) and
the red-necked (miconax, nancymaae,
nigriceps, azarae and subspecies), found south of the
Rio Amazonas (Groves 2001). Because this change in taxonomy was
introduced fairly recently and is disputed, some published research
continues to refer to the entire group as A. trivirgatus rather
than distinguishing among species and subspecies. It may be necessary
to generalize about some of the characteristics of owl monkeys because
of the confusion of taxonomy in the literature in addition to the
limited published information about this taxonomic group (Wright 1994;
Separated into two groups based on their coloration,
geographic distribution, owl monkeys have gray-tan to brown bodies and
either gray or red fur on the sides of their necks (Ford 1994). They
have pale yellow to orange fur on their stomachs, underarms, and inner
legs, light gray to white markings above and below their eyes, and three
conspicuous, black stripes from the top of their head to either side of
each eye and straight down the forehead between the eyes to the bridge
of the nose (Ford 1994; Rowe 1996; Groves 2001). Their coats range in
thickness and length depending on the altitudes at which they are found,
with species living at higher elevations having thicker, shaggier coats
than those living at sea level (Wright 1981; Groves 2001). They are
unusual in their appearance compared to other primates because of their
disproportionately large, brown eyes which have evolved as an adaptation
to their nocturnal lifestyles. All owl monkeys are at least somewhat nocturnal and they
are the only New World
monkeys active at night (Wright 1994). While a nocturnal lifestyle is associated
with primitive primates like prosimians,
owl monkeys are not primitive
but rather they re-evolved nocturnality from diurnal ancestors (Wright 1994; Rowe
1996). Changes in the morphology
of the eye and brain of owl monkeys reveal how specialized they have
become to keep this nocturnal lifestyle but also reveal structural
commonalities between other diurnal primates (Rowe 1996). To see
objects in low light levels, owl monkeys have evolved large eyeballs,
their lenses have a more spherical shape than is seen in diurnal
primates, and there are also more rods
and fewer cones (Noback 1975).
Though they do see in color, owl monkeys have less acute color vision
than other primates. This is not a disadvantage as they are faster at
locating and following moving objects at low light levels and have better
spatial resolution at low light levels than other primates which helps
them capture insects and move through
arboreal habitat (Wright 1994).
Photo: Luiz Claudio Marigo
There is very limited data on body size and weight for Aotus, most measurements from wild animals are extrapolated from only a few samples.
Owl monkeys are not sexually dimorphic so
males and females are about the same size and weight (Wright 1994). Average male A. a. azarae weigh about 1254 g (2.76 lb)
while females average 1246 g (2.75 lb). Wild A. a. boliviensis males weigh, on average 1180 g (2.60 lb) while females are
slightly heavier, having an average weight of 1230 (2.71 lb) (Fernandez-Duque in press). The weights from one wild A. a.
infulatus male and one female are 1190 g (2.62 lb) and 1240 g (2.73 lb), respectively, and data from one male and one
female A. brumbacki reveal weights of 875 g (1.93 lb) and 455 g (1.00 lb) (Fernandez-Duque in press). Data from wild
A. lemurinus reveal an average male weight of 920.7 g (2.03 lb) and average female weight of 859 g (1.89 lb). The weight
of one male A. nigriceps was 875 g and the average weight of two females was 1040 g (2.29 lb). There is a fair amount of
information available on the body weights of A. nancymaae and A. trivirgatus. A. nancymaae males weigh, on average, 794
g (1.75 lb) and females weigh 780 g (1.72 lb) while wild A. trivirgatus males weigh, on average 813 g (1.79 lb) and females
average 736 g (1.62 lb) (Fernandez-Duque in press). The weights of wild A. vociferans and A. zonalis are also based on
small sample sizes. Male A. vociferans weigh 697.5 g (1.54 lb) and there are no data for wild females while A. zonalis males
have an average weight of 889 g (1.96 lb) and females weight 916 g (2.02 lb), on average (Fernandez-Duque in press).
There are no data available for A. miconax.
Owl monkeys move quadrupedally on branches and vines
in the forests in which they live and are skilled leapers, able to cross
gaps in the canopy up to four meters wide (Wright 1984). The maximum
recorded longevity for a captive owl monkey is 20 years (Rowe 1996).
The only data on their longevity in the wild comes from an A. azarae population where it is known that a male has lived at least 11 years (Fernandez-Duque pers. comm.).
CURRENT RANGE MAPS (IUCN REDLIST):Aotus azarae
| Aotus hershkovitzi
| Aotus lemurinus
| Aotus miconax
| Aotus nancymaae
| Aotus nigriceps
| Aotus trivirgatus
| Aotus vociferans
Owl monkeys are widely distributed across southern Central America and
northern South America (Groves 2001). A. lemurinus subspecies
are found in Panama, northern Colombia, and northwestern Venezuela while
A. hershkovitzi ranges only in Colombia. The other gray-necked
species include A. trivirgatus, which occupies a range
extending from eastern Colombia and southern Venezuela into part of
northern Brazil and A. vociferans, which is widely distributed
across Colombia, northern Brazil, northern Peru, and eastern Ecuador
(Groves 2001). All of the gray-necked species live north of the Amazon
River while the red-necked owl monkeys are found south of the Amazon.
A. miconax is limited to a very small region in northwestern
Peru; A. nancymaae occupies a small region straddling the
Peru-Brazil border and is sympatric with both red-necked (A.
nigriceps) and gray-necked species (A. vociferans); A.
nigriceps is found in Brazil and Peru, and A. azarae subspecies
are found in Paraguay, Argentina, southern Bolivia, and Brazil (Groves
2001; Fernandez-Duque et al. 2001).
Little research has been conducted on Aotus in the wild
probably primarily due to the difficulty of studying nocturnal primates
(Sussman 2000). Research on owl monkeys requires not only specialized
forest skills, including the ability to maneuver through the forest at
night and good auditory and nocturnal visual skills, but radio-tracking
equipment as well (Sussman 2000; Aquino & Encarnación 1994).
Some of the intrepid owl monkey researchers and contributors to the
knowledge of wild Aotus include Patricia Wright (Peru and
Paraguay), Rolando Aquino and Filomeno Encarnación (Peru), and
Eduardo Fernandez-Duque (Argentina). Captive studies of Aotus
have been conducted at the New England Primate Research Center.
Aotus species widely inhabit primary, secondary, and remnant tropical forests as well as
seasonally deciduous scrub forest, subtropical dry forest, and gallery
forest from Panama to Argentina and Paraguay at a wide variety of
elevations from sea level to 3200 m (10,498 ft) (Wright 1981; Aquino &
Encarnación 1994; Fernandez-Duque et al. 2001). Temperatures at higher
elevations can be as low as 5° C (41° F) and in the Chaco of
Argentina, night temperatures as low as -5° C (23° F)
are tolerated by Aotus (Fernandez-Duque 2003). They tend to inhabit
areas of high plant species diversity with a relatively dense canopy and
will forage at all canopy levels (Kinzey 1997). In Peru, they
specifically prefer two types of habitats: lowland forest that is flooded
seasonally or highland forest that is never flooded. In the flooded
forest, where water can be as deep as seven meters (23.0 ft) during the rainy
season, there is a predominance of trees with thickened trunks and
branches that provide hollows used as sleeping sites, as well as
pervasive growth of lianas and epiphytes, important plants used as
sleeping sites and refuges (Aquino & Encarnación 1994). In
Colombia, Aotus species are found in high, primary forests and in remnant and
older secondary forests, but not in young secondary forests with low
species diversity. In Argentina, Aotus is found in both high
and low forests as well as gallery and island
forests with dense
canopies (Wright 1981; Fernandez-Duque et al. 2001). In Brazil, A. infulatus uses a variety
of habitats including coastal forests with palm trees, mangroves, and
gallery forest (de Sousa e Silva & Fernandes 1999). All of the
habitats in which they are found exhibit seasonal patterns of rainfall
and temperature changes, with the rainy season generally lasting from
about September to about May and the dry season occurring during June
through August (Wright 1981).
Aotus is the only nocturnal monkey. Adopting a system of
nocturnal behavior seems disadvantageous to animals like primates that
have a high dependence on vision: food, including insects, animal prey,
and fruit, is more difficult to find at night, locomotion through the
forest canopy is significantly more dangerous in dim light, and a
different set of environmental conditions such as cooler temperatures,
differences in humidity, competitors, and predators pose threats (Wright
1989). Despite these obstacles, the fossil record proves that owl
monkeys assumed this nocturnal role from diurnal ancestors and, based on
their wide geographical distribution, have been successful in exploiting
this niche. Many of the ecological and behavioral characteristics of
Aotus can be explained or at least linked to their unique
pattern of life. Though most species of owl monkeys are nocturnal,
A. a. azarae shows the particularly rare pattern of cathemeral
activity in which it is regularly active during both daylight and
nighttime hours (Fernandez-Duque 2003). Because of its range in the
very seasonal Chaco of Argentina and Paraguay, the ability to forage
during daylight hours is probably an adaptation to avoid activity on
extremely cold, moonless nights (Fernandez-Duque 2003).
Photo: Marilyn Cole
Members of the genus generally leave their sleeping site about 15
minutes after sunset and return before sunrise each day (Wright 1986; Garcia & Braza 1993).
After leaving the sleeping site, groups travel and feed until about
midnight, when they stop to rest for 90 to 120 minutes. Owl monkeys are
frugivores and supplement their
diet with flowers, insects, nectar, and leaves (Wright 1989; 1994).
They prefer small, ripe fruit when available and in order to find these,
they forage in large-crown trees (larger than ten meters [32.8 ft]) (Wright 1986).
Seasonal availability of fruit varies across environments.
Aotus species in tropical forests eat more fruit throughout the
year because it is more readily available compared to the dry forests
where fruit is limited in the dry season and owl monkeys are more
dependent on leaves (Wright 1994). It is difficult to quantify leaf and insect eating
during the night, though, and researchers sometimes have to rely on fecal sample
composition to project quantity and therefore importance to owl monkeys.
Insect foraging occurs at dawn and dusk. Rather than seeking out insects in holes and crevices, owl
monkeys are adept at grabbing flying insects out of the air or snatching
them off of a branch (Wright 1989). They most often eat large orthopterans, moths, beetles, and
spiders and probably specialize in these because of the insects'
rhythms. Moths are active at night, orthopterans call loudly at night,
exposing their location, and beetles are active at night are easier
making them easier to see (Wright 1989). After spending the
night traveling, foraging, resting, and socializing, as dawn approaches
owl monkeys increase their activity levels, and forage as they travel to
either the same sleeping site from the previous day or another one
within their home range (Wright 1981). Sleeping sites are either tree
holes or thickets of dense foliage made up of lianas or epiphytes and,
if they are big enough, may be shared with other nocturnal animals like
bats (Aquino & Encarnación 1986; Garcia & Braza 1993).
Owl monkeys spend most of their time foraging and sleeping above in the
high canopy, above ten meters (32.8 ft) (Wright 1994).
Density of owl monkeys ranges from two to
16 groups per km² (.772 to 6.18 groups per square mile) (Fernandez-Duque
et al. 2001). Home ranges of owl monkeys are smallranging between .031 and
.175 km² (.012 and .068 mi²), depending on the species (Fernandez-Duque in press).
The average nightly range is about of 708 m per night (.441 mi), but they use
a larger area during the wet season, 829 m (.515 mi) per night and a smaller
area during the dry season, 252 m (.157 mi) (Wright 1989). This use of space
indicates that they spend more time resting and rely on fewer resources during
the dry season, but resource availability is not the only factor influencing
nightly travel distance. Nightly path length is also correlated with
available light; the distance traveled is directly linked to the amount
of moonlight on a given night. Owl monkeys travel twice as far on
bright nights with full moons than on dark nights, and they concentrate
their movement during the times of night with the most moonlight (Wright
1989; Fernandez-Duque 2003). Even though they do not travel as far,
they still need to move on dark nights to find food and one adaptation
to this need to forage is to travel the same routes repeatedly. They
probably memorize routes and use chemical cues to help them find their
way between food sites and sleeping sites (Wright 1989).
Aotus azarae azarae
Photo: Eduardo Fernandez Duque
Though owl monkeys are sympatric with other primates that use similar
resources, they do not compete for access to resources because of their
alternative schedules. Furthermore, non-primate nocturnal competitors
are usually small-bodied (like bats) or forage alone or in pairs, not
posing a significant source of competition (Wright 1989). Nocturnal
predators do not usually eat monkeys, but some potential threats include
owls, snakes, and felids. Diurnal
raptors may pose a threat to owl monkeys if they are not well hidden in
their sleeping sites (Wright 1989; 1994).
At any given time, there are about 150 to 200 million people worldwide
infected with malaria and over a million children annually under the age of five
die from this disease spread by infected mosquitoes (Dixson 1994). Owl
monkeys have been successfully employed in biomedical research on
malaria since the 1960s because of their natural resistance to the
parasites that cause the disease (Ford 1994). Individuals of some
species are intermittently removed from the wild to bolster captive
colonies for research, breeding programs, and zoos, but effects on the
total population are not significant and the population can recover
after these "cropping" events (Aquino & Encarnación 1994).
Content last modified: July 18, 2005
Written by Kristina Cawthon Lang. Reviewed by Eduardo Fernandez-Duque.
Cite this page as:
Cawthon Lang KA. 2005 July 18. Primate Factsheets: Owl monkey (Aotus) Taxonomy, Morphology, & Ecology . <http://pin.primate.wisc.edu/factsheets/entry/owl_monkey>. Accessed 2015 January 28.