ANDEAN NIGHT MONKEY
Geographic Distribution and Habitat
Andean night monkeys (Aotus miconax), also known as Peruvian night monkeys, are endemic to the South American country of Peru, in the Andes Mountains. They are found between elevations of 2,600 to 10,200 feet (800–3,100 meters) in the humid cloud forests of the mountains. In some cases, Andean night monkeys are able to live in disturbed habitat such as coffee plantations.
Andean night monkeys are part of the Aotus genus, commonly known as the night monkeys. The species in this genus are the world’s only truly nocturnal monkeys. Until the 1980s, all Aotus monkeys were considered the same species. Today, most sources cite ten or eleven species in Aotus. Many researchers believe that number is an underestimate, not truly reflective of the large amount of diversity seen in the genus. Species in Aotus are often divided up as either red-necked or gray-necked, with Andean night monkeys in the former group. Andean night monkeys are one of the least studied species in Aotus.
Size, Weight, and Lifespan
Adult Andean night monkeys weigh up to 2.5 lbs (1.1 kg) and measure up to 20 inches (50 cm) in length, including their long tails. The oldest recorded night monkey in the wild was 13 years old. In captivity, the oldest recorded age was 20 years.
Upon first glance, one might assume an Andean night monkey is a prosimian, more at home in the tropics of Madagascar than in the cloud forests of the Andes Mountains. However, the Andean night monkey’s large eyes and small size—features seen in many prosimians—are evolutionary adaptations that allow them to take advantage of their nighttime niche without being a large target for the many nocturnal (nighttime) predators they share a habitat with.
“Aotus” means “without ears,” which, while not true, may seem true at first glance, as their small ears are not immediately visible within the dense fur surrounding their head. Their round faces have a striking black and white pattern that frames their large brown eyes.
Their small bodies are mostly gray, with a large rusty orange patch taking up the entirety of their bellies and inner arms. They have long tails that help them maintain their balance as they climb about the canopy, as well as padded, claw-like fingers that help them grip onto tree branches. Males and females look very much alike, as they are not sexually dimorphic.
Andean night monkeys have a varied diet, although close to half (42% according to one study) is composed of fruit. Plant buds make up another 25% of their diet, with the rest being composed of flowers, leaves, and insects. Figs are a particularly favored food of night monkeys.
Daily Life and Group Dynamics
Andean night monkeys are monogamous and live in groups of up to six individuals—one adult pair and their offspring. The offspring may be composed of an infant, one or two juveniles, and sometimes a sub-adult. It is unknown whether Andean night monkeys are truly monogamous or just socially monogamous—that is, whether adults copulate with others than their mate. Solitary individuals, likely young adults that have recently left their natal group and have not yet established their own family group, have also been observed. Their home ranges are relatively small, and they travel up to half a mile (0.8 km) in a typical night. Home ranges tend to be smaller during the dry season and larger during the wet season.
The genus “Aotus” means “without ears.” While that’s not true, it may seem true at first glance, as night monkeys’ small ears can be lost in their dense hair!
As their name would suggest, Andean night monkeys are nocturnal, with their most active period being at the beginning of the night. They are arboreal (tree-dwelling) and spend their days sleeping in tree hollows, amid vines, or in piles of leaves and sticks. They awake shortly after sunset, and this is their most active period of the day. They spend the night traveling and feeding, with a rest period around midnight. They find another sleep site shortly before the sun rises. One study found that they spend about 54% of their time traveling, 13% resting, and 33% feeding, with more active nights when there is brighter moonlight. They often travel the same routes to find food. Some researchers have speculated that this large percentage of traveling time may be in response to their degraded habitat, as they must travel longer distances to find resources in degraded habitat. They tend to move rather slowly, even being described as “sluggish,” and usually stick to the upper canopy region of the forest.
While there is little information available related to Andean night monkey communication, night monkeys in general use a large array of vocal and chemical cues to communicate, with some sources citing as many as 50 different vocalizations! These include what have been described as squeaks, hisses, and barks, and their throat sac can be expanded to make their calls even louder. Their alarm call has been described as a “wook.” They use scent glands located on their throat and the base of their tail to mark their environment and communicate to other Andean night monkeys, as well as practice “urine washing,” in which they coat their hands and feet with urine, which scent the environment as they walk about. Curiously, Andean night monkeys are not known to exhibit some common bonding behaviors, such as allogrooming, although they are known to play with groupmates.
Both males and females use mating calls to find their mates, and both initiate copulation through sexual vocalizations. If copulation results in pregnancy, the female will be pregnant for approximately 122 to 153 days, or roughly four months, after which she gives birth to a single infant. While there is no strict birthing season, more births tend to happen at the beginning of the rainy season. Males play the dominant role in child rearing early on, being the primary infant carrier, feeder (after the baby is weaned), protector, and playmate to the baby. The baby is nursed by its mother to about seven months of age. The baby is independent at about a year of age and reaches sexual maturity at about two years of age. Both males and females disperse from their natal group.
Little is known about the predators of Andean night monkeys, although they likely include owls, arboreal snakes, and big cats, as well as birds of prey or other diurnal (daytime) predators that discover their sleeping sites. Generally speaking, their nocturnality, tendency to stick to the high canopy, and cryptic coloring likely keeps them relatively safe. Andean night monkeys are themselves predators to the small invertebrates they eat, and likely play a role in seed dispersal due to the fruit they eat. They are sympatric with two other primate species: the Peruvian yellow-tailed woolly monkey (Oreonax flavicauda) and the Andean titi monkey (Callicebus oenanthe). As these species are both diurnal, they likely do not interact often or compete very heavily for resources with Andean night monkeys.
Andean night monkeys are categorized as Endangered by the International Union for Conservation of Nature (IUCN, 2019), appearing on the IUCN’s Red List of Threatened Species. This dire assessment is due to a substantial population loss, which is believed to be over 50% of their historic population. The population decline is largely due to the corresponding 50% loss of habitat, as well as habitat exploitation, over the past ten years, both of which are expected to continue in the future.
Peru has experienced rampant deforestation, habitat disturbance, and significant hunting pressure in its recent history. One study found that suitable Andean night monkey habitat has declined by nearly 50% of its original extent. Prior to the 1970s, the cloud forests in the Andean foothills were virtually inaccessible to humans, but since then, the ever-encroaching highway system has brought immigration further into the foothills, and with it, habitat loss. This habitat loss is primarily the result of expansions in mining, large-scale farming, and cattle ranching. While Andean night monkeys are known to be flexible with their habitat requirements—one study followed a family group living in a forest fragment only 3.4 acres (1.4 hectares) large—they are by no means immune to the rampant habitat destruction they are experiencing. And just because the animals may survive in a fragmented forest doesn’t mean they are thriving. A concern of many researchers is in improving connectivity between forest fragments to encourage gene flow, which would help mitigate the effects of inbreeding depression.
Hunting pressure is high, especially as people immigrate into new areas. Young Andean night monkeys are often taken as pets by hunters and sold illegally. One small study mentioned the numerous Andean night monkeys that local interviewees kept as pets in nearby towns.
Andean night monkeys are listed on Appendix II of the Convention on International Trade in Endangered Species (CITES) and is considered Endangered under Peruvian law. They are protected by several public protected areas, including Abiseo National Park and the Alto Mayo Protection Forest, as well as a number of private protected areas.
- Cornejo, F., R. Aquino, C. Jimenez. 2008. Notes on the Natural History, Distribution and Conservation Status of the Andean Night Monkey. Primate Conservation, 23(1):1-4.
- Shanee, S. and N. Shanee. 2011. Observations of Terrestrial Behavior in the Peruvian Night Monkey (Aotus miconax) in an Anthropogenic Landscape, La Esperanza, Peru. Neotropical Primates, 18(2):55-58.
- Shanee, S, N. Shanee, N. Allgas-Marchena. 2013. Primate surveys in the Maranon-Huallaga landscape, northern Peru with notes on conservation. Primate Conservation, 27: 3-11.
Written by K. Clare Quinlan, July 2021