Night Monkeys (Aotidae)
Night monkeys
(Aotidae)
Class Mammalia
Order Primates
Family Aotidae
Thumbnail description
Gracile monkeys with a slender body and a rounded head; face flat with short muzzle; nocturnal habits reflected by remarkably large eyes, resulting in the alternate name "owl monkeys," and inconspicuous pelage coloration
Size
Medium-sized monkeys weighing approximately 2 lb (910 g)
Number of genera, species
1 genus; 8 species
Habitat
Evergreen tropical rainforest, gallery forest, and mixed deciduous forest
Conservation status
Vulnerable: 2 species; Data Deficient 1 species
Distribution
After howler monkeys (genus Alouatta), this is the second most widely distributed genus among the New World monkeys, occurring over a vast range including Panama and a large part of South America
Evolution and systematics
Traditionally, only a single night monkey species (Aotus trivirgatus) was recognized, but chromosomal evidence revealed considerable diversity. This is hardly surprising, given the extensive geographical range covered by Aotus. It is now widely accepted that there are between five and nine night monkey species, and eight species can be recognized as a basic minimum. Night monkeys provide a graphic example of a persistent failure to recognize cryptic species among nocturnal primates, because they differ relatively little in visually obvious characters. Molecular evidence indicates that some individual night monkey species diverged at a very early stage and also suggests that there is no close relationship between the night monkey lineage and any other group of New World monkeys. It is hence appropriate to recognize a separate family Aotidae for the night monkeys, rather than just a subfamily (Aotinae). It has been customary to include the titi monkeys (genus Callicebus) with the night monkeys in the subfamily Aotinae, but molecular evidence does not indicate any phylogenetic association between Aotus and Callicebus, so there is no justification for classifying these two genera together.
The night monkeys can be divided into a gray-neck group of four species occurring essentially north of the River Amazon (Aotus hershkovitzi, Aotus lemurinus, Aotus trivirgatus and Aotus vociferans) and a red-necked group of four species occurring almost exclusively south of the Amazon (Aotus azarai, Aotus miconax, Aotus nancymaae and Aotus nigriceps).
As is the case for New World monkeys, generally, there is very little fossil evidence to document the evolution of night monkeys. However, some fragmentary remains from the early Miocene of the La Venta site in Colombia have been allocated to a species in the modern genus Aotus (Aotus dindinensis). The lower jaw and teeth closely resemble those of the modern night monkey and a fragment of the skull indicates that large eyes were present, suggesting that nocturnal habits were already present as in living species.
Physical characteristics
The body is slender and covered with dense fine hair, varying in color from gray to brown dorsally and from yellow to
orange ventrally. Conspicuous white or pale gray patches surround the eyes and the mouth, and the white areas above the eyes are emphasized to varying extents by three spurs of dark fur in the midline and on either side of the crown. The head is rounded and the muzzle does not protrude. The tail, which is not prehensile, is typically longer than the body and densely furred. Average head and body length is 13.5 in (34 cm); average tail length is 15 in (37 cm). There is no sexual dimorphism in size and the average body mass for both sexes is approximately 2 lb (910 g).
Distribution
Widely distributed in Central and South America, from the foothills of the Andes eastward. Occurs in Panama, Nicaragua, Colombia, Peru, Bolivia, Brazil, Venezuela, and Paraguay.
Habitat
Wide distribution throughout evergreen tropical rainforests and certain dry forest areas, between sea level and 10,700 ft (3,200 m).
Behavior
Uniquely among higher primates, night monkeys are typically nocturnal, although cathemeral activity (mixed day and night activity) has been reported for some populations. Several lines of evidence indicate that they have become secondarily adapted for nocturnal life, following divergence from a diurnal ancestor. During the daytime, they typically sleep in tree hollows. Their basal metabolism is relatively low and this is reflected in quite sluggish movement and limited ranging during the nocturnal phase of activity. Olfactory marking is performed with urine and with marking glands. There is a small marking gland on the chest and a diffuse glandular area on the underside of the tail base. Night monkeys also perform "urine washing," in which the palms of the hands and the soles of the feet are impregnated with urine that is then deposited during locomotion.
Feeding ecology and diet
Primarily consume fruits, with a supplement of arthropods (mainly insects) and perhaps small vertebrates and eggs.
Reproductive biology
Field studies have consistently indicated that night monkeys are monogamous, living in pairs along with any immature offspring. The testes are relatively small and spermatogenesis seems to take place with a remarkably low turnover. For Aotus lemurinus griseimembra, the ovarian cycle is 15–16 days long and the gestation period was found to be 133 days from a single timed mating. The latter figure is likely to apply to all night monkeys, as an overall range of gestation periods of 122–141 days has been reported for a captive colony containing Aotus azarai, A. lemurinus, A. nancymaae, and A. vociferans. Single births are typical. The infant is carried clinging to an adult's fur, and both parents participate in infant carriage.
Conservation status
Two species are listed as Vulnerable (Aotus lemurinus, A. miconax); one species is Data Deficient (A. hershkovitzi).
Significance to humans
Because of their nocturnal habits, night monkeys are relatively protected from human interference, but they may occasionally be hunted for food. Several night monkey species have been used in medical research, notably because they can be infected with human malaria.
Species accounts
List of Species
Gray-bellied night monkeyNancy Ma's night monkey
Three-striped night monkey
Gray-bellied night monkey
Aotus lemurinus
subfamily
Aotinae
taxonomy
Aotus lemurinus (I. Geoffroy, 1843), Quindio, Dept. of Caldas, Colombia. Originally included in the species Aotus trivirgatus, the gray-bellied night monkey is now allocated to the separate species Aotus lemurinus, containing 4 subspecies (lemurinus, brumbacki, griseimembra, and zonalis). It is quite possible that one or more of these subspecies may actually be a full species, and that one may be the same as A. lemurinus lemurinus.
other common names
English: Gray-bellied owl monkey, gray-bellied douroucouli; French: Douroucouli à ventre gris; German: Graubauchnachtaffe.
physical characteristics
Fur gray to buff-agouti dorsally and yellow to pale orange ventrally. Because of previous uncertainty over taxonomy, no reliable data on body dimensions are available for this species alone. Body mass: males 2 1b (920 g); females 1 lb 15 oz (875 g).
distribution
Panama, northern Colombia, and northwestern Venezuela.
habitat
Predominantly evergreen tropical rainforest, including montane forest.
behavior
Nocturnal. Little-studied in the wild.
feeding ecology and diet
Feeds primarily on fruits with a supplement of arthropods (mainly insects).
reproductive biology
Presumably monogamous. Ovarian cycle 15–16 days long; gestation period approximately 133 days. Single births are typical, but twins often occur.
conservation status
Listed as Vulnerable.
significance to humans
Occasionally hunted for food. Used quite extensively for medical research.
Nancy Ma's night monkey
Aotus nancymaae
subfamily
Aotinae
taxonomy
Aotus nancymaae Hershkovitz, 1983, Loreto, Peru. Originally included in the species Aotus trivirgatus but recognized as a separate species because of chromosomal features.
other common names
English: Nancy Ma's owl monkey, Nancy Ma's douroucouli; French: Douroucouli de Nancy Ma; German: Nancy Ma-Nachtaffe.
physical characteristics
Fur gray-agouti dorsally and pale orange ventrally. Facial fur pale gray with three dark brown stripes on the crown. Head and body length: 12.5 in (31 cm); tail length: 15 in (38 cm). Body mass: males 1 lb 12 oz (794 g); females 1 lb 12 oz (780 g).
distribution
Occupies a limited range spanning the border between Peru and Brazil, essentially confined between the Amazon/Marañon in the north and the Juruá in the south.
habitat
Evergreen tropical rainforest.
behavior
Nocturnal. Little-studied in the wild.
feeding ecology and diet
Presumably feeds primarily on fruits with a supplement of arthropods (mainly insects).
reproductive biology
Presumably monogamous. Ovarian cycle probably 15–16 days long; gestation period probably approximately 133 days. Single births are typical.
conservation status
Not regarded as currently threatened.
significance to humans
Occasionally hunted for food.
Three-striped night monkey
Aotus trivirgatus
subfamily
Aotine
taxonomy
Aotus trivirgatus (Humboldt, 1811), Rio Casiquiare, Duida Range, Venezuela. This species once included all night monkeys but it is now restricted to just one of at least 8 species occupying a far smaller geographical range.
other common names
English: Three-striped douroucouli; French: Douroucouli à trois raies; German: Dreistreifennachtaffe.
physical characteristics
Fur gray to buff-agouti dorsally and bright orange ventrally.
Facial fur pale gray; stripes on crown brown. Conspicuous orange band down the middle of the back. Because of previous uncertainty over taxonomy, no reliable data on body dimensions are available for this species alone. Body mass: males 1 lb 13 oz (810 g); females 1 lb 10 oz (735 g).
distribution
Eastern Colombia, southern Venezuela and part of northern Brazil above the River Amazon.
habitat
Predominantly evergreen tropical rainforest.
behavior
Nocturnal. Little-studied in the wild.
feeding ecology and diet
Presumably feeds primarily on fruits with a supplement of arthropods (mainly insects).
reproductive biology
Presumably monogamous. Ovarian cycle probably 15–16 days long; gestation period presumably approximately 133 days. Single births are typical.
conservation status
Not threatened.
significance to humans
Occasionally hunted for food. Used quite frequently for medical research.
| Common name / Scientific name | Physical characteristics | Habitat and behavior | Distribution | Diet | Conservation status |
| Hershkovitz's night monkey Aotus hershkovitzi | Pelage is short, dense, semiwoolly, soft. Silver gray to dark gray, underparts brownish. Three dark brown or black lines on face. Small ears, densely furred tail. Head and body length 9.4–14.6 in (24–37 cm), tail length 12.4–15.7 in (31.6–40 cm). | Can be found in forests from sea level to about 6,890 ft (2,100 m). Nocturnal. | Colombia, Dept. of Meta, east side of Cordillera Oriental. | Consists mainly of fruits, nuts, leaves, bark, flowers, gums, insects, and small vertebrates. | Data Deficient |
| Noisy night monkey Aotus vociferans | Pelage is short, dense, semiwoolly, soft. Silver gray to dark gray, underparts brownish. Three dark brown or black lines on face. Small ears, densely furred tail. Head and body length 9.4–14.6 in (24–37 cm), tail length 12.4–15.7 in (31.6–40 cm). Solimões Rivers). | Can be found in forests from sea level to about 6,890 ft (2,100 m). Nocturnal. | Colombia, east of Cordillera Oriental, west of Rio Negro, south to Brazil (north of Amazon-Consists mainly of fruits, nuts, leaves, bark, flowers, gums, insects, and small vertebrates. | Not threatened | |
| Azari's night monkey Aotus azarai | Pelage is short, dense, semiwoolly, soft. Silver gray to dark gray, underparts brownish. Three dark brown or black lines on face. Small ears, densely furred tail. Head and body length 9.4–14.6 in (24–37 cm), tail length 12.4–15.7 in (31.6–40 cm). | Can be found in forests from sea level to about 6,890 ft (2,100 m). Nocturnal. | Bolivia south of Rio Madre de Dios, south to Paraguay and northern Argentina. | Consists mainly of fruits, nuts, leaves, bark, flowers, gums, insects, and small vertebrates. | Not threatened |
| Andean night monkey Aotus miconax | Pelage is short, dense, semiwoolly, soft. Silver gray to dark gray, underparts brownish. Three dark brown or black lines on face. Small ears, densely furred tail. Head and body length 9.4–14.6 in (24–37 cm), tail length 12.4–15.7 in (31.6–40 cm). | Can be found in forests from sea level to about 6,890 ft (2,100 m). Nocturnal. | A small area in Peru between Rio Ucayali and the Andes, south of Rio Marañon. | Consists mainly of fruits, nuts, leaves, bark, flowers, gums, insects, and small vertebrates. | Vulnerable |
| Black-headed night monkey Aotus nigriceps | Pelage is short, dense, semiwoolly, soft. Silver gray to dark gray, underparts brownish. Three dark brown or black lines on face. Small ears, densely furred tail. Head and body length 9.4–4.6 in (24–37 cm), tail length 12.4–15.7 in (31.6–40 cm). | Can be found in forests from sea level to about 6,890 ft (2,100 m). Nocturnal. | Brazil, south of Rio Solimões, west of Rio Tapajós Juruena, west into Peru. | Consists mainly of fruits, nuts, leaves, bark, flowers, gums, insects, and small vertebrates. | Not threatened |
Resources
Books
Baer, Janet F., Richard E. Weller, and Ibulaimu Kakoma, eds. Aotus: The Owl Monkey. San Diego: Academic Press, 1994.
Dixson, Alan F. "The Owl Monkey (Aotus trivirgatus)." In Reproduction in New World Primates, edited by John P. Hearn. Lancaster: MTP Press, 1982.
Dixson, Alan F., Rosemary C. Bonney, Dirk Fleming, and Robert D. Martin. "Reproductive Biology of the Owl Monkey Aotus trivirgatus griseimembra." In Non-Human Primate Models in Human Reproduction, edited by T. C. Anand Kumar. Basel: Karger, 1980, pp. 61–68.
Groves, Colin P. Primate Taxonomy. Washington, DC: Smithsonian Institute Press, 2001.
Napier, Prudence H. Catalogue of Primates in the British Museum (Natural History) and Elsewhere in the British Isles. Part I: Families Callitrichidae and Cebidae. London: British Museum (Natural History), 1976.
Wright, Patricia C. "The Night Monkeys, Genus Aotus." In Ecology and Behavior of Neotropical Primates, Vol. 1, edited by Adelmar F. Coimbra-Filho and Russell A. Mittermeier. Rio de Janeiro: Academia Brasileira de Ciências, 1981, pp. 211–240.
Periodicals
Aquino, R., and F. Encarnacion. "Population densities and geographic distribution of night monkeys (Aotus nancymai and Aotus vociferans) (Cebidae, Primates) in northeastern Peru." American Journal of Primatology 14 (1988): 375–381.
Ashley, M. V., and J. L. Vaughn. "Owl monkeys (Aotus) are highly divergent in mitochondrial cytochrome c oxidase (COII) sequences." International Journal of Primatology 16 (1995): 793–806.
Canavez, F. C., M. M. Moreiera, J. J. Ladasky, A. Pissinati, P. Parham, and H. Seuánez. "Molecular phylogeny of New World primates (Platyrrhini) based on beta2-microglobin DNA sequences." Molecular Phylogenetics and Evolution 12 (1999): 74–82.
Dixson, A. F., and D. Fleming. "Parental behaviour and infant development in owl monkeys (Aotus trivirgatus griseimembra)." Journal of Zoology, London 194 (1981): 25–39.
Galbreath, G. J. "Karyotypic evolution in Aotus." American Journal of Primatology 4 (1983): 245–251.
Gozalo, A., and E. Montoya. "Reproduction of the owl monkey (Aotus nancymai) (Primates: Cebidae) in captivity." American Journal of Primatology 21 (1990): 61–68.
Hershkovitz, Phillip. "Two new species of night monkeys, genus Aotus (Cebidae, Platyrrhini): A preliminary report on Aotus taxonomy." American Journal of Primatology 4 (1983): 209–243.
Horovitz, I., R. Zardoya, and A. Meyer. "Platyrrhine systematics: A simultaneous analysis of molecular and morphological data." American Journal of Physical Anthropology 106 (1998): 261–281.
Hunter, J. M., R. D. Dixson, F. Alan, and B. C. C. Rudder. "Gestation and inter-birth intervals in the owl monkey (Aotus trivirgatus griseimembra)." Folia Primatology 31 (1979): 165–175.
Le Maho, Y., M. Goffart, A. Rochas, H. Felbabel, and J. Chatonnet. "Thermoregulation in the only nocturnal simian: the night monkey Aotus trivirgatus." American Journal of Physiology 240 (1981) R156–R165.
Ma, N. S. F., R. N. Rossan, S. T. Kelley, J. S. Harper, M. T. Bedard, and T. C. Jones. "Banding patterns of the chromosomes of two new karyotypes of the owl monkey, Aotus, captured in Panama." Journal of Medical Primatology 7 (1978): 146–155.
Malaga, C. A., R. E. Weller, R. L. Buschbom, J. F. Baer, and B. B. Kimsey. "Reproduction of the owl monkey (Aotus sp.) in captivity." Journal of Medical Primatology 26 (1997): 147–152.
Martin, R. D. "Long night for owl monkeys." Nature 326 (1987): 639–640.
Setoguchi, T., and A. L. Rosenberger. "A fossil owl monkey from La Venta, Colombia." Nature 326 (1987): 692–694.
Smith, R. J., and W. L. Jungers. "Body mass in comparative primatology." Journal of Human Evolution 32 (1997): 523–559.
Torres, O. M., S. Enciso, F. Ruiz, E. Silva, and I. Yunis. "Chromosome diversity of the genus Aotus from Colombia." American Journal of Primatology 44 (1998): 255–275.
Wright, P. C. "Home range, activity pattern and agonistic encounters of a group of night monkeys (Aotus trivirgatus) in Peru." Folia Primatology 29 (1978): 43–55.
Robert D. Martin, PhD