Night monkeys, also known as owl monkeys or douroucoulis (), are nocturnal
New World monkey
New World monkeys are the five families of primates that are found in the tropical regions of Mexico, Central and South America: Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae. The five families are ranked together as the Ceboidea ...
s of the
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
''Aotus'', the only member of the
family
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
Aotidae (). The genus comprises eleven species which are found across Panama and much of South America in primary and secondary forests, tropical rainforests and cloud forests up to . Night monkeys have large eyes which improve their vision at night, while their ears are mostly hidden, giving them their name ''Aotus'', meaning "earless".
Night monkeys are the only truly nocturnal monkeys with the exception of some
cathemeral
Cathemerality, sometimes called metaturnality, is an organismal activity pattern of irregular intervals during the day or night in which food is acquired, socializing with other organisms occurs, and any other activities necessary for livelihood ar ...
populations of
Azara's night monkey
Azara's night monkey (''Aotus azarae''), also known as the southern night monkey, is a night monkey species from South America. It is found in Argentina, Bolivia, Brazil, Peru and Paraguay. The species is monogamous, with the males providing a ...
, who have irregular bursts of activity during day and night. They have a varied repertoire of vocalisations and live in small family groups of a
mated pair
Breeding pair is a pair of animals which cooperate over time to produce offspring with some form of a bond between the individuals.Gaston, A. J.The evolution of group territorial behavior and cooperative breeding" The American Naturalist 112.988 ...
and their immature offspring. Night monkeys have monochromatic vision which improves their ability to detect visual cues at night.
Night monkeys are threatened by habitat loss, the pet trade, hunting for bushmeat, and by biomedical research. They constitute one of the few monkey species that are affected by the often deadly human
malaria
Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. S ...
protozoan '' Plasmodium falciparum'', making them useful as non-human primate experimental subjects in malaria research. The
Peruvian night monkey
The Peruvian night monkey (''Aotus miconax''), also known as the Andean night monkey, is a nocturnal New World monkey endemic to northern Peru. Adults weigh around and measure up to in length. Its colour is grey to light brown with characteris ...
is classified by the
International Union for Conservation of Nature
The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of nat ...
Vulnerable species
A vulnerable species is a species which has been categorized by the International Union for Conservation of Nature as being threatened with extinction unless the circumstances that are threatening its survival and reproduction improve.
Vulnera ...
, four are
Least-concern species
A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. T ...
, and two are data deficient.
Taxonomy
Until 1983, all night monkeys were placed into only one (''A. lemurimus'') or two species (''A. lemurinus'' and ''A. azarae''). Chromosome variability showed that there was more than one species in the genus and Hershkovitz (1983) used morphological and karyological evidence to propose nine species, one of which is now recognised as a junior synonym. He split ''Aotus'' into two groups: a northern, gray-necked group ('' A. lemurinus'', '' A. hershkovitzi'', '' A. trivirgatus'' and '' A. vociferans'') and a southern, red-necked group ('' A. miconax'', '' A. nancymaae'', '' A. nigriceps'' and '' A. azarae''). Arguably, the taxa otherwise considered subspecies of ''A. lemurinus'' – '' brumbacki'', '' griseimembra'' and '' zonalis'' – should be considered separate species, whereas '' A. hershkovitzi'' arguably is a junior synonym of ''A. lemurinus''. A new species from the gray-necked group was recently described as '' A. jorgehernandezi''. As is the case with some other splits in this genus, an essential part of the argument for recognizing this new species was differences in the
chromosomes
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
. Chromosome evidence has also been used as an argument for merging "species", as was the case for considering ''infulatus'' a subspecies of ''A. azarae'' rather than a separate species. One extinct species is known from the
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
record.
Classification
Family Aotidae
*Genus ''Aotus''
** ''Aotus lemurinus'' (gray-necked) group:
***
Gray-handed night monkey
The gray-handed night monkey (''Aotus griseimembra'') is a species of night monkey formerly considered a subspecies of Gray-bellied night monkey of the family Aotidae. Its range consists of parts of Colombia and Venezuela. The exact classificati ...
Brumback's night monkey
Brumback's night monkey (''Aotus brumbacki'') is a species of night monkey found in Colombia. It has traditionally been considered a subspecies of gray-bellied night monkey
The gray-bellied night monkey (''Aotus lemurinus''), also called the g ...
, ''Aotus brumbacki''
***
Three-striped night monkey
The three-striped night monkey (''Aotus trivirgatus''), also known as northern night monkey or northern owl monkey, is one of several species of owl monkeys currently recognised. It is found in Venezuela and north-central Brazil.
Until 1983, all ...
, ''Aotus trivirgatus''
***
Spix's night monkey
Spix's night monkey (''Aotus vociferans''), also known as the Colombian gray night monkey, noisy night monkey and Spix's owl monkey, is a night monkey species from South America. It is found in Brazil, Colombia, Ecuador and Peru.
The Spix's nigh ...
Azara's night monkey
Azara's night monkey (''Aotus azarae''), also known as the southern night monkey, is a night monkey species from South America. It is found in Argentina, Bolivia, Brazil, Peru and Paraguay. The species is monogamous, with the males providing a ...
, ''Aotus azarae''
***
Peruvian night monkey
The Peruvian night monkey (''Aotus miconax''), also known as the Andean night monkey, is a nocturnal New World monkey endemic to northern Peru. Adults weigh around and measure up to in length. Its colour is grey to light brown with characteris ...
, ''Aotus miconax''
***
Nancy Ma's night monkey
Nancy Ma's night monkey (''Aotus nancymaae'') is a night monkey species from South America. It is found in Brazil and Peru.
It is known in medical research as a model organism
A model organism (often shortened to model) is a non-human spec ...
, ''Aotus nancymaae''
***
Black-headed night monkey
The black-headed night monkey (''Aotus nigriceps'') is a night monkey species from South America. It is found in Brazil, Bolivia and Peru. The ''A. nigriceps'' in Peru were notably inhabiting areas that were degraded, and often these areas were ...
, ''Aotus nigriceps''
**Group ''
Incertae sedis
' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...
''
***''
Aotus dindensis
''Aotus dindensis'' is an extinct species of New World monkeys in the genus '' Aotus'' from the Middle Miocene (Laventan in the South American land mammal ages; 13.8 to 11.8 Ma). Its remains have been found at the Konzentrat-Lagerstätte of La ...
''
Physical characteristics
Night monkeys have large brown eyes; the size improves their nocturnal vision increasing their ability to be active at night. They are sometimes said to lack a
tapetum lucidum
The ''tapetum lucidum'' ( ; ; ) is a layer of tissue in the eye of many vertebrates and some other animals. Lying immediately behind the retina, it is a retroreflector. It reflects visible light back through the retina, increasing the light a ...
, the reflective layer behind the retina possessed by many nocturnal animals. Other sources say they have a tapetum lucidum composed of collagen fibrils. At any rate, night monkeys lack the tapetum lucidum composed of riboflavin crystals possessed by lemurs and other
strepsirrhines
Strepsirrhini or Strepsirhini (; ) is a suborder of primates that includes the lemuriform primates, which consist of the lemurs of Madagascar, galagos ("bushbabies") and pottos from Africa, and the lorises from India and southeast Asia. Colle ...
, which is an indication that their nocturnalitiy is a secondary adaption evolved from ancestral diurnal primates.
Their ears are rather difficult to see; this is why their genus name, ''Aotus'' (meaning "earless") was chosen. There is little data on the weights of wild night monkeys. From the figures that have been collected, it appears that males and females are similar in weight; the heaviest species is
Azara's night monkey
Azara's night monkey (''Aotus azarae''), also known as the southern night monkey, is a night monkey species from South America. It is found in Argentina, Bolivia, Brazil, Peru and Paraguay. The species is monogamous, with the males providing a ...
at around , and the lightest is
Brumback's night monkey
Brumback's night monkey (''Aotus brumbacki'') is a species of night monkey found in Colombia. It has traditionally been considered a subspecies of gray-bellied night monkey
The gray-bellied night monkey (''Aotus lemurinus''), also called the g ...
, which weighs between . The male is slightly taller than the female, measuring , respectively.
Ecology
Night monkeys can be found in
Panama
Panama ( , ; es, link=no, Panamá ), officially the Republic of Panama ( es, República de Panamá), is a transcontinental country spanning the southern part of North America and the northern part of South America. It is bordered by Co ...
Ecuador
Ecuador ( ; ; Quechua: ''Ikwayur''; Shuar: ''Ecuador'' or ''Ekuatur''), officially the Republic of Ecuador ( es, República del Ecuador, which literally translates as "Republic of the Equator"; Quechua: ''Ikwadur Ripuwlika''; Shuar: ' ...
,
Peru
, image_flag = Flag of Peru.svg
, image_coat = Escudo nacional del Perú.svg
, other_symbol = Great Seal of the State
, other_symbol_type = National seal
, national_motto = "Firm and Happy f ...
,
Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
,
Paraguay
Paraguay (; ), officially the Republic of Paraguay ( es, República del Paraguay, links=no; gn, Tavakuairetã Paraguái, links=si), is a landlocked country in South America. It is bordered by Argentina to the south and southwest, Brazil to th ...
,
Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
Venezuela
Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in th ...
. The species that live at higher elevations tend to have thicker fur than the monkeys at sea level. Night monkeys can live in forests undisturbed by humans (
primary forest
An old-growth forestalso termed primary forest, virgin forest, late seral forest, primeval forest, or first-growth forestis a forest that has attained great age without significant disturbance, and thereby exhibits unique ecological feature ...
) as well as in forests that are recovering from human logging efforts ( secondary forest).
Distribution
A primary distinction between red-necked and gray-necked night monkeys is spatial distribution. Gray-necked night monkeys (''Aotus lemurinus'' group) are found north of the Amazon River, while the red-necked group (''Aotus azare'' group) are localized south of the Amazon River. Red-necked night monkeys are found throughout various regions of the Amazon rainforest of South America, with some variation occurring between the four species.
Nancy Ma's night monkey
Nancy Ma's night monkey (''Aotus nancymaae'') is a night monkey species from South America. It is found in Brazil and Peru.
It is known in medical research as a model organism
A model organism (often shortened to model) is a non-human spec ...
occurs in both flooded and unflooded tropical rainforest regions of Peru, preferring moist swamp and mountainous areas. This species has been observed nesting in regions of the Andes and has recently been introduced to Colombia, likely as a result of post-research release into the community. The
black-headed night monkey
The black-headed night monkey (''Aotus nigriceps'') is a night monkey species from South America. It is found in Brazil, Bolivia and Peru. The ''A. nigriceps'' in Peru were notably inhabiting areas that were degraded, and often these areas were ...
is also found mainly in the Peruvian Amazon (central and upper Amazon), however its range extends throughout Brazil and Bolivia to the base of the Andes mountain chain. Night monkeys such like the black-headed night monkey, generally inhabit cloud forests; areas with consistent presence of low clouds with a high mist and moisture content which allows for lush and rich vegetation to grow year round, providing excellent food and lodging sources. The
Peruvian night monkey
The Peruvian night monkey (''Aotus miconax''), also known as the Andean night monkey, is a nocturnal New World monkey endemic to northern Peru. Adults weigh around and measure up to in length. Its colour is grey to light brown with characteris ...
, like Nancy Ma's night monkey, is endemic to the Peruvian Andes however it is found at a higher elevation, approximately above sea level and therefore exploits different niches of this habitat. The distribution of ''A. azare'', extends further towards the Atlantic Ocean, spanning Argentina, Bolivia and the drier, south western regions of Paraguay, however unlike the other red-necked night monkey species, it is not endemic to Brazil.
Sleep sites
During the daylight hours, night monkeys rest in shaded tree areas. These species have been observed exploiting four different types of tree nests, monkeys will rest in; holes formed in the trunks of trees, in concave sections of branches surrounded by creepers and epiphytes, in dense areas of epiphyte, climber and vine growth and in areas of dense foliage. These sleeping sites provide protection from environmental stressors such as heavy rain, sunlight and heat. Sleeping sites are therefore carefully chosen based upon tree age, density of trees, availability of space for the group, ability of site to provide protection, ease of access to the site and availability of site with respect to daily routines. While night monkeys are an arboreal species, nests have not been observed in higher strata of the rainforest ecosystem, rather a higher density of nests were recorded at low-mid vegetation levels. Night monkeys represent a territorial species, territories are defended by conspecifics through the use of threatening and agonistic behaviours. Ranges between night monkey species often do overlap and result in interspecific aggressions such as vocalizing and chasing which may last up to an hour.
Diet
Night monkeys are primarily frugivorous (fruit eating species) as fruits are easily distinguished through the use of olfactory cues, but leaf and insect consumption has also been observed in the cathemeral night monkey species ''A. azare''. A study conducted by Wolovich et al., indicated that juveniles and females were much better at catching both crawling and flying insects than adult males. In general, the technique used by night monkeys in insect capturing is to use the palm of the hand to flatten a prey insect against a tree branch and then proceed to consume the carcass. During the winter months or when food sources are reduced, night monkeys have also been observed foraging on flowers such as ''Tabebuia heptaphylla'', however this does not represent a primary food source.
Reproduction
In night monkeys, mating occurs infrequently, however females are fertile year-round, with reproductive cycles range from 13 to 25 days. The gestation period for night monkey is approximately 117– 159 days but varies from species to species. Birthing season extends from September to March and is species dependant, with one offspring being produced per year; however, in studies conducted in captivity, twins were observed. Night monkeys reach puberty at a relatively young age, between 7– 11 months and most species attain full sexual maturity by the age of 2 years of age. ''A. azare'' represents an exception reaching sexual maturity by the age of 4.
Behavior
The name "night monkey" comes from the fact that all species are active at night and are, in fact, the only truly nocturnal monkeys (an exception is the subspecies of
Azara's night monkey
Azara's night monkey (''Aotus azarae''), also known as the southern night monkey, is a night monkey species from South America. It is found in Argentina, Bolivia, Brazil, Peru and Paraguay. The species is monogamous, with the males providing a ...
, ''Aotus azarae azarae'', which is
cathemeral
Cathemerality, sometimes called metaturnality, is an organismal activity pattern of irregular intervals during the day or night in which food is acquired, socializing with other organisms occurs, and any other activities necessary for livelihood ar ...
). Night monkeys make a notably wide variety of vocal sounds, with up to eight categories of distinct calls (gruff grunts, resonant grunts, sneeze grunts, screams, low trills, moans, gulps, and hoots), and a frequency range of 190–1,950 Hz. Unusual among the New World monkeys, they are monochromats, that is, they have no colour vision, presumably because it is of no advantage given their nocturnal habits. They have a better spatial resolution at low light levels than other primates, which contributes to their ability to capture insects and move at night. Night monkeys live in family groups consisting of a mated pair and their immature offspring. Family groups defend
territories
A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal.
In international politics, a territory is usually either the total area from which a state may extract power resources or a ...
by vocal calls and
scent marking
In ethology, territory is the sociographical area that an animal consistently defends against conspecific competition (or, occasionally, against animals of other species) using agonistic behaviors or (less commonly) real physical aggression. ...
.
The night monkey is socially monogamous, and all night monkeys form
pair bond
In biology, a pair bond is the strong affinity that develops in some species between a mating pair, often leading to the production and rearing of offspring and potentially a lifelong bond. Pair-bonding is a term coined in the 1940s that is freque ...
s. Only one infant is born each year. The male is the primary caregiver, and the mother carries the infant for only the first week or so of its life. This is believed to have developed because it increases the survival of the infant and reduces the metabolic costs on the female. Adults will occasionally be evicted from the group by same-sex individuals, either kin or outsiders.
Nocturnality
The family ''Aotidae'' is the only family of nocturnal species within the suborder Anthropoidea. While the order primates is divided into prosimians; many of which are nocturnal, the anthropoids possess very few nocturnal species and therefore it is highly likely that the ancestors of the family ''Aotidae'' did not exhibit nocturnality and were rather diurnal species. The presence of nocturnal behavior in ''Aotidae'' therefore exemplifies a derived trait; an evolutionary adaptation that conferred greater fitness advantages onto the night monkey. Night monkey share some similarities with nocturnal prosimians including low basal metabolic rate, small body size and good ability to detect visual cues at low light levels. Their responses to olfactory stimulus are intermediate between those of the prosimians and diurnal primate species, however the ability to use auditory cues remains more similar to diurnal primate species than to nocturnal primate species. This provides further evidence to support the hypothesis that nocturnality is a derived trait in the family ''Aotidae''.
As the ancestor of ''Aotidae'' was likely diurnal, selective and environmental pressures must have been exerted on the members of this family which subsequently resulted in the alteration of their circadian rhythm to adapt to fill empty niches. Being active in the night rather than during the day time, gave ''Aotus'' access to better food sources, provided protection from predators, reduced interspecific competition and provided an escape from the harsh environmental conditions of their habitat. To begin, resting during the day allows for decreased interaction with diurnal predators. Members of the family ''Aotidae,'' apply the predation avoidance theory, choosing very strategic covered nests sites in trees. These primates carefully choose areas with sufficient foliage and vines to provide cover from the sun and camouflage from predators, but which simultaneously allow for visibility of ground predators and permit effective routes of escape should a predator approach too quickly. Activity at night also permits night monkeys to avoid aggressive interactions with other species such as competing for food and territorial disputes; as they are active when most other species are inactive and resting.
Night monkeys also benefit from a nocturnal life style as activity in the night provides a degree of protection from the heat of the day and the thermoregulation difficulties associated. Although night monkey, like all primates are endothermic, meaning they are able to produce their own heat, night monkeys undergo behavioural thermoregulation in order to minimize energy expenditure. During the hottest points of the day, night monkeys are resting and therefore expending less energy in the form of heat. As they carefully construct their nests, night monkeys also benefit from the shade provided by the forest canopy which enables them to cool their bodies through the act of displacing themselves into a shady area. Additionally, finding food is energetically costly and completing this process during the day time usually involves the usage of energy in the form of calories and lipid reserves to cool the body down. Foraging during the night when it is cooler, and when there is less competition, supports the optimal foraging theory; maximize energy input while minimizing energy output.
While protection from predators, interspecific interactions, and the harsh environment propose ultimate causes for nocturnal behavior as they increase the species fitness, the proximate causes of nocturnality are linked to the environmental effects on circadian rhythm. While diurnal species are stimulated by the appearance of the sun, in nocturnal species, activity is highly impacted by the degree of moon light available. The presence of a new moon has correlated with inhibition of activity in night monkeys who exhibit lower levels of activity with decreasing levels of moon light. Therefore, the lunar cycle has a significant influence on the foraging and a nocturnal behaviors of night monkey species.
Pair-bonded social animals (social monogamy)
Night monkeys are socially monogamous—they form a bond and mate with one partner. They live in small groups consisting of a pair of reproductive adults, one infant and one to two juveniles. These species exhibit mate guarding, a practice in which the male individual will protect the female he is bonded to and prevent other conspecifics from attempting to mate with her. Mate guarding likely evolved as a means of reducing energy expenditure when mating. As night monkey territories generally have some edge overlap, there can be a large number of individuals coexisting in one area which may make it difficult for a male to defend many females at once due to high levels of interspecific competition for mates. Night monkeys form bonded pairs and the energy expenditure of protecting a mate is reduced. Pair bonding may also be exhibited as a result of food distribution. In the forest, pockets of food can be dense or very patchy and scarce. Females, as they need energy stores to support reproduction are generally distributed to areas with sufficient food sources. Males will therefore also have to distribute themselves to be within proximity to females, this form of food distribution lends itself to social monogamy as finding females may become difficult if males have to constantly search for females which may be widely distributed depending on food availability that year.
However, while this does explain social monogamy, it does not explain the high degree of paternal care which is exhibited by these primates. After the birth of an infant, males are the primary carrier of the infant, carrying offspring up to 90% of the time. In addition to aiding in child care, males will support females during lactation through sharing their foraged food with lactating females. Generally, food sharing is not observed in nature as the search for food requires a great degree of energy expenditure, but in the case of night monkey males, food sharing confers offspring survival advantages. As lactating females may be too weak to forage themselves, they may lose the ability to nurse their child, food sharing therefore ensures that offspring will be well feed. The act of food sharing is only observed among species where there is a high degree of fidelity in paternity. Giving up valuable food sources would not confer an evolutionary advance unless it increased an individual's fitness; in this case, paternal care ensures success of offspring and therefore increases the father's fitness.
Olfactory communication and foraging
Recent studies have proposed that night monkeys rely on olfaction and olfactory cues for foraging and communication significantly more than other diurnal primate species. This trend is reflected in the species physiology; members of Aotidae possess larger scent perception organs than their diurnal counterparts. The olfactory bulb, accessory olfactory bulb and volume of lateral olfactory tract are all larger in ''Aotus'' than in any of the other new world monkey species. It is therefore likely that increased olfaction capacities improved the fitness of these nocturnal primate species; they produced more offspring and passed on these survival enhancing traits. The benefits of increased olfaction in night monkeys are twofold; increased ability to use scent cues has facilitated night time foraging and is also an important factor in mate selection and sexual attractivity.
As a substantial portion of the night monkey's activities occurring during the dark hours of the night, there is a much lower reliance of visual and tactile cues. When foraging at night, members of the family Aotidae will smell fruits and leaves before ingesting to determine the quality and safety of the food source. As they are highly frugivorous and cannot perceive colour well, smell becomes the primary determinant of the ripeness of fruits and is therefore an important component in the optimal foraging methods of these primates. Upon finding a rich food source, night monkeys have been observed scent marking not only the food source, but the route from their sleeping site to the food source as well. Scent can therefore be used as an effective method of navigation and reduce energy expenditure during subsequent foraging expeditions. Night monkeys possess several scent glands covered by greasy hair patches, which secrete pheromones that can be transferred onto vegetation or other conspecifics. Scent glands are often located subcaudal, but also occur near the muzzle and the sternum. The process of scent marking is accomplished through the rubbing of the hairs covering scent glands onto the desired “marked item”.
Olfactory cues are also of significant importance in the process of mating and mate guarding. Male night monkeys will rub subcaudal glands onto their female partner in a process called “partner marking” in order to relay the signal to coexisting males that the female is not available for mating. Night monkeys also send chemical signals through urine to communicate reproductive receptivity. In many cases, male night monkeys have been observed drinking the urine of their female mate; it is proposed that the pheromones in the urine can indicate the reproductive state of a female and indicate ovulation. This is especially important in night monkeys as they cannot rely on visual cues, such as the presence of a tumescence, to determine female reproductive state. Therefore, olfactory communication in night monkeys is a result of sexual selection; sexually dimorphic trait conferring increased reproductive success. This trait demonstrates sexual dimorphism, as males have larger subcaudal scent glands compare to female counterparts and sex differences have been recorded in the glandular secretions of each gender. There is a preference for scents of a particular type; those which indicate reproductive receptivity, which increases species fitness by facilitating the production of offspring.
Conservation
According to the IUCN (the
International Union for Conservation of Nature
The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of nat ...
), the
Peruvian night monkey
The Peruvian night monkey (''Aotus miconax''), also known as the Andean night monkey, is a nocturnal New World monkey endemic to northern Peru. Adults weigh around and measure up to in length. Its colour is grey to light brown with characteris ...
Least-concern species
A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. T ...
, and two are data deficient. Most night monkey species are threatened by varying levels of habitat loss throughout their range, caused by
agricultural expansion
Agricultural expansion describes the growth of agricultural land (arable land, pastures, etc.) especially in the 20th and 21st centuries.
The agricultural expansion is often explained as a direct consequence of the global increase in food and en ...
, cattle ranching, logging, armed conflict, and mining operations. To date, it is estimated that more than 62% of the habitat of the
Peruvian night monkey
The Peruvian night monkey (''Aotus miconax''), also known as the Andean night monkey, is a nocturnal New World monkey endemic to northern Peru. Adults weigh around and measure up to in length. Its colour is grey to light brown with characteris ...
has been destroyed or degraded by human activities. However, some night monkey species have become capable of adapting exceptionally well to anthropogenic influences in their environment. Populations of Peruvian night monkey have been observed thriving in small forest fragments and plantation or farmland areas, however this is likely possible given their small body size and may not be an appropriate alternate habitat option for other larger night monkey species. Studies have already been conducted into the feasibility of agroforestry; plantations which simultaneously support local species biodiversity. In the case of ''A. miconax'', coffee plantations with introduced shade trees, provided quality habitat spaces. While the coffee plantation benefited from the increased shade—reducing weed growth and desiccation, night monkeys used the space as a habitat, a connection corridor or stepping stone area between habitats that provided a rich food source. However, some researchers question the agroforestry concept, maintaining that monkeys are more susceptible to hunting, predator and pathogens in plantation fields, thus indicating the need for further research into the solution before implementation.
Night monkeys are additionally threatened by both national and international trade for bushmeat and domestic pets. Since 1975, the pet trade of night monkeys has been regulated by CITES (the Convention on International Trade in Endangered Species). In the last forty years, nearly 6,000 live night monkeys and more than 7,000 specimens have been traded from the nine countries which they call home. While the restrictive laws put into place by CITES are aiding in the reduction of these numbers, 4 out of 9 countries, show deficiencies in maintaining the standards outlined by CITES Increased attention and enforcement of these laws will be imperative for the sustainability of night monkey populations.
Use in biomedical research poses another threat to night monkey biodiversity. Species such as
Nancy Ma's night monkey
Nancy Ma's night monkey (''Aotus nancymaae'') is a night monkey species from South America. It is found in Brazil and Peru.
It is known in medical research as a model organism
A model organism (often shortened to model) is a non-human spec ...
, like human beings, are susceptible to infection by the '' Plasmodium falciparum'' parasite responsible for malaria. This trait caused them to be recommended by the World Health Organization as test subjects in the development of malaria vaccines. Up to 2008, more than 76 night monkeys died as a result of vaccine testing; some died from malaria, while others perished due to medical complications from the testing.
Increased research and knowledge of night monkey ecology is an invaluable tool in determining conservation strategies for these species and raising awareness for consequences of the anthropogenic threats facing these primates. Radio-collaring of free ranging primates proposes a method of obtaining more accurate and complete data surrounding primate behavior patterns. This in turn can aid in understanding what measures need to be taken to promote the conservation of these species. Radio collaring not only allows for the identification of individuals within a species, increased sample size, more detailed dispersal and range patterns, but also facilitates educational programs which raise awareness for the current biodiversity crisis. The usage of radio-collaring while potentially extremely valuable, has been shown to interfere with social group interactions, the development of better collaring techniques and technology will therefore be imperative in the realisation and successful use of radio collars on night monkeys.