Owl Monkeys

Family Nyctipithecidae (Gray, 1870)

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Owl Monkeys, also known as Night Monkeys, or Douroucoulis are the world's only nocturnal monkeys. They form monogamous pairs in which males are the primary caregivers - unlike more than 90% of all mammals. Aotus is the most widely distributed of the new world monkeys, ranging from Panama to Argentina. Despite this, their survival is threatened by habitat loss, subsistance hunting, and capture for use in pharmesutical research.

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Taxonomy

Owl Monkeys are members of the Genus Aotus, which is monotypic in the Family Nyctipithecidae. This genus consists of ten known species, divided into two groups: the "Gray-neck," found north of the Amazon and the "Red-neck," found to the south. This division is also due to malaria susceptability (the Red- necked group is resistant) and chromosomal variations.

Physical Description

Owl monkeys weigh approximately 1 kg (Napier & Napier, 1996), and are not sexually dimorphic. Eyes are large, brown, and unlike other nocturnal mammals, lack a tapetum lucidum (a light-gathering layer). Also unusual for a nocturnal mammal, Owl Monkeys have color vision. Ears are small, and difficult to see (Aotus means "earless"). Their long, thin digits have straight nails and wide fingertip pads. Two toes posses curved nails, which may be grooming nails similar to those found in prosimians (Wright, 1985).

Coats are short, thick, and counter shaded: a greyish brown dorsally and yellow tan ventrally. Their faces have dark stripes, and a white patch over each eye. These patches may create an illusion of alertness even when eyes are closed (Moynihan, 1976). The throat and sides of the neck vary in color from gray in the northern species to red in the southern species. Their nonprehensile tail is nearly as long as their body, with varying amounts of black at the tip.

Locomotion

Owl monkeys are quadrupedal (walking and leaping) and arboreal, and their tail acts as a counter balance as they move through the trees (Wright, 1985).

Habitat & Distribution

Owl Monkeys are the most widely distributed of the new world primates. Their range extends from southern Panama to northern Argentina, and from eastern Brazil to western Peru (Robinson et al., 1987). Habitat generalists, they are found anywhere from lowland dry forests to montane cloud forests at elevations up to 3200m (10,499ft) (Rowe, 1996), and they occupy nearly all forest levels from 7 to 35 m (Wright, 1981). They sleep in tree holes and vine tangles, choosing concealed sleeping spots due both to the threat of predators and proximity to food sources (Heymann, 1995).

Owl monkeys are nocturnal, and they are usually most active one hour after dusk and one hour before dawn, and more than twice as active during a full moon (Erkert and Grober, 1986). Nocturnality may have developed in part as a response to the threat of predation - diurnal predators are more likely to eat monkeys than nocturnal predators. In regions with few diurnal predators, Owl monkeys may be cathermal, and active for as many as three hours during the day. Studies in the lowland dry forests of Paraguay and Argentina have found this to be the case with A. azarae (Wright, 1996).

Diet

Owl monkeys eat fruits (65-70%), insects (5-20%) and leaves (5-30%) (Rowe, 1996). Approximately 50% of its waking hours are spent foraging and 80% of that time eating fruit (Wright, 1985). The owl monkey is an important dispersal agent; seeds pass unharmed through the gut (Wright, 1985). In the dry season, when fruit becomes scarce, nectar becomes an important food source and takes up 30% of their foraging time. Figs also form a large part of the dry season diet. Nocturnality decreases competition with diurnal frugivores and takes advantage of the availability of the larger nocturnal insects as a food source (Wright, 1989). Insects occupy 15 to 20% of feeding time year-round (Wright, 1985).

Development

• Infant: 0-8mo.
• Weaning: 8mo.
• Juvenile: 8mo. - 2 years
• Subadult: 2-3 years
• Gestation: 127 days
• Birthing Season: January-February
• Birth Interval: 5.5-14mo.
• Life Span: 20 years
  

Owl monkeys have one of the shortest gestations of the neotropical primates. Interbirth intervals are relatively short (less than one year) due to high levels of paternal care. Males begin carrying their young the day of their birth and continue to do so up to 80% of the time for the first 5 months (Wright, 1985). Females feed their infants every few hours, but have little interaction with them otherwise. Females will even bite their infant on the tail, hands or feet until it returns to the male (Dixson, 1994).

There are two birth peaks: one at the end of the dry season and the other in the middle of the wet season (Wright, 1985). Sexually mature at 2 1/2 years, young males and females disperse within the next six months (Wright, 1985). The males may travel on their own before pair-bonding with a female (Charles-Dominique, 1977).

Social Structure

• Group Size: 3-5
• Home Range: 3ha (7acres)
• Night Range: 252-829m (827-2720ft)

The night monkey is most often monogamous, with groups consisting of one male, one female, and up to three offspring. Highly territorial, males and females share offspring/territory defense. Male and female intergroup interactions may last up to fifteen minutes and include vocalizations, wrestling, and chasing.

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... This article is incomplete ...

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