Douroucouli / Northern owl monkey (Aotus trivirgatus)
Douroucoulis are the only nocturnal monkeys. Unlike the nocturnal prosimians, they do not have a reflective layer in their eyes to help them see in the dark. They are adapted to nightlife in that they have large eyes and are most active during the full moon, when they can see better what's going on!
Physical description: Douroucoulis are grey with yellowish bellies and big brown eyes. A strip of black runs down their forehead, between white arches above each eye. They have tiny pink ears hidden by dense fur. A characteristic owl monkey expression is to look around curiously with their heads cocked to the side. Their facial markings give them the impression of wearing a permanent smile. Douroucoulis weigh just under 1kg and are about 70cm from the tip of the tail to the top of their head, with the tail making up more than half of this length.
Habitat: Douroucoulis live in primary to secondary forest, but also dry forest if there is enough fruit to be found. This species can be found in Colombia, Venezuela and Brazil. Other species of owl monkey are found from Panama until as far south as Argentina. They inhabit a variety of forests and are often found near human settlements.
Diet: These monkeys have been observed to feed on fruit, flowers, leaves and insects (including moths, beetles, spiders and cicadas). However, detailed analysis of their diet has not been carried out, since they are so difficult to study due to their nocturnal habits. It seems that fruit is their favourite food and this is also what they eat most of at Monkeyland.
Life history: Douroucoulis have a gestation period of just over four months and an average birth interval of ten months. They generally have one offspring at a time, although twins were observed on two rare occasions in captivity. Births normally take place in early spring. These primates reach sexual maturity somewhere between the age of 2-4 years and females usually have their first offspring by 3-5 years, but this information varies greatly from what is known in captivity and the few studies of wild animals.
Associations: There are no other nocturnal monkeys, so even if douroucoulis share their habitat with other monkeys, they are never awake at the same time and therefore presumably do not interact with each other.
Social structure: Group size ranges between 2-6 individuals, consisting of a monogamous pair and their dependent offspring. However, solitary individuals can also be encountered, who are usually young adults that have not yet started a family or elderly animals that were evicted from their group. One of the parents is quite often replaced by an incoming individual who fights for access to the group. Unlike in many other animal species, an invasive male will not kill the offspring from the real father. Quite to the contrary, he cares for them as though they were his own. Nonetheless, juveniles often chose to leave with their evicted father instead.
Territorial marking: Douroucoulis mark their territories both with urine and with secretions from scent-glands. Smell seems to be very important to these animals, since aggression is usually preceded by some sort of smelly communication. In a captive study, owl monkeys males whose noses were blocked displayed less aggression towards each other.
Communication: The vocalisations of douroucoulis can be divided into eight distinct categories. Their most recognisable sounds are the called whoops and hoots. Whoops are loud noises made by both males and females during aggressive encounters. Hoots are low-frequency calls that appear to transmit information over long distances. Owl monkeys are particularly vocal around full moon, when they are most active.
Mating: Although the reproductive cycle of female douroucoulis lasts approximately 16 days, mating is very rarely observed. One study of wild groups recorded only 8 mating occasions after 2,000 hours of observation over the course of 3 years. In captivity, mating was only observed slightly more often.
Other behaviour: Douroucoulis are one of a few primate species where fathers invest a large amount of time in caring for the young. The young are only carried by the mother for the first few weeks of life, then the father takes over this role. The male also plays with the young, grooms them and shares food with them.
During the day, douroucoulis sleep in vine tangles or in tree hollows. Only one species of douroucouli is sometimes active during the day, and they live furthest away from the equator in the Gran Chaco of Argentina, where night time temperatures may simply be too cold for them to be able to survive on foraging exclusively at night.
Conservation: They are classed as lower risk/least concern by the IUCN since they are "a wide-ranging species with no evidence of any particular threat other than habitat loss" (which is significant throughout their range). However, all douroucoulis across South America were traditionally presumed to belong to the same species. More recent analysis, including DNA sampling, revealed that there are at least 7 different species. Studies of the abundance of each individual species have not been performed since this is a very difficult task for nocturnal primates that cannot be easily spotted. It seems that the distribution of some of these species is rather tiny, so they may go extinct before they are even officially accepted as a separate species.
Did you know? Douroucoulis have a grooming claw on the fourth digit of each foot.
Defler, T.R., Rodr�guez-M., J.V. & Brazil Threatened Species Workshop participants 2003. Aotus trivirgatus. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 16 July 2006.
Fernandez-Duque, E. (2006) Aotinae: Social Monogamy in the Only Nocturnal Haplorhines. In: Campbell et al. (eds.), Primates in Perspective. New York/Oxford: Oxford University Press.
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