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{{Short description|Genus of New World monkeys}}
{{for|the persona briefly adopted by Peter Parker in the MCU|Spider-Man: Far From Home}}
{{for|the raccoon relative that shares the same common name|Ringtail}}
{{Automatic taxobox
| name = Night monkeys<ref name=msw3>{{MSW3 Primates | id = 12100299 | pages = 139–141}}</ref>
| image = Panamanian night monkey.jpg
| image_caption = A [[Panamanian night monkey]] in Panama [[File:Night Monkey (Aotus azarae) (W AOTUS AZARAE R1 C1).ogg|thumb|left|Night monkey calls, recorded in Madre de Dios, Peru]]
| display_parents = 3
| parent_authority = [[Poche (zoologist)|Poche]], 1908 (1865)
| taxon = Aotus
| authority = [[Johann Karl Wilhelm Illiger|Illiger]], 1811
| type_species = ''[[Three-striped night monkey|Simia trivirgata]]''
| type_species_authority = [[Alexander von Humboldt|Humboldt]], 1811
| subdivision_ranks = [[Species]]
| subdivision = [[#Taxonomy|see text]]
}}

'''Night monkeys''', also known as '''owl monkeys''' or '''douroucoulis'''<ref>{{cite EB1911 |wstitle=Douroucouli |volume=8 |page=450}}</ref> ({{IPAc-en|d|uː|r|uː|'|k|uː|l|i|z}}), are nocturnal [[New World monkey]]s of the [[genus]] '''''Aotus''''', the only living member of the [[family (biology)|family]] '''Aotidae''' ({{IPAc-en|eɪ|'|ɒ|t|ᵻ|d|iː}}). 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 {{convert|2400|m|ft}}. 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, although some [[Cathemerality|cathemeral]] populations of [[Azara's night monkey]] have irregular bursts of activity during day and night. They have a varied repertoire of vocalisations and live in small family groups of a [[pair bonding|mated pair]] and their immature offspring. Night monkeys have [[monochromacy|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 affected by the often deadly human [[malaria]] [[protozoan]] ''[[Plasmodium falciparum]]'' and are therefore used as experimental subjects in malaria research. The [[Peruvian night monkey]] is classified by the [[International Union for Conservation of Nature]] (IUCN) as an [[Endangered species]], while four are [[Vulnerable species]], four are [[Least-concern species]], and two are data deficient.

==Taxonomy==
Until 1983, all night monkeys were placed into only one (''A. lemurinus'') 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]].<ref name= Defler2007/> He split ''Aotus'' into two groups: a northern, gray-necked group (''[[Gray-bellied night monkey|A. lemurinus]]'', ''[[Gray-bellied night monkey|A. hershkovitzi]]'', ''[[Three-striped night monkey|A. trivirgatus]]'' and ''[[Spix's night monkey|A. vociferans]]'') and a southern, red-necked group (''[[Peruvian night monkey|A. miconax]]'', ''[[Nancy Ma's night monkey|A. nancymaae]]'', ''[[Black-headed night monkey|A. nigriceps]]'' and ''[[Azara's night monkey|A. azarae]]'').<ref name=msw3/> Arguably, the taxa otherwise considered subspecies of ''A. lemurinus'' – ''[[Aotus brumbacki|brumbacki]]'', ''[[Aotus griseimembra|griseimembra]]'' and ''[[Aotus zonalis|zonalis]]'' – should be considered separate species,<ref name= Defler2001>{{cite journal | author = Defler, T.R. | author2 = Bueno, M. L. | author3 = Hernández-Camacho, J. I. | name-list-style = amp | year = 2001 | title = The taxonomic status of ''Aotus hershkovitzi'': Its relationship to ''Aotus lemurinus lemurinus'' | journal = Neotropical Primates | volume = 9 | issue = 2 | pages = 37–52| doi = 10.62015/np.2001.v9.480 | doi-access = free }}</ref><ref name= Defler2007/> whereas ''[[Aotus hershkovitzi|A. hershkovitzi]]'' arguably is a [[junior synonym]] of ''A. lemurinus''.<ref name= Defler2001/> A new species from the gray-necked group was recently described as ''[[Aotus jorgehernandezi|A. jorgehernandezi]]''.<ref name="Defler2007">{{cite journal | last1 = Defler | first1 = T. R. | last2 = Bueno | first2 = M. L. | year = 2007 | title = ''Aotus'' diversity and the species problem | journal = Primate Conservation | volume = 2007 | issue = 22 | pages = 55–70 | url = http://www.primate-sg.org/storage/PDF/PC22.jorgehernandezi.V2.pdf | doi=10.1896/052.022.0104| s2cid = 56262730 | doi-access = free }}</ref> As is the case with some other splits in this genus,<ref>{{cite journal | author = Torres, O. M. | author2 = Enciso, S. | author3 = Ruiz, F. | author4 = Silva, E. | author5 = Yunis, I. |name-list-style = amp | year = 1998 | title = Chromosome diversity of the genus ''Aotus'' from Colombia | journal = American Journal of Primatology |volume = 44 | issue = 4 | pages = 255–275 | doi = 10.1002/(SICI)1098-2345(1998)44:4<255::AID-AJP2>3.0.CO;2-V | pmid = 9559066| s2cid = 25955413 }}</ref> an essential part of the argument for recognizing this new species was differences in the [[chromosomes]].<ref name= Defler2007/> 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.<ref>{{cite journal | author = Pieczarka, J. C. | author2 = de Souza Barros, R. M. | author3 = de Faria Jr, F. M. | author4 = Nagamachi, C. Y. | year = 1993 | title = ''Aotus'' from the southwestern Amazon region is geographically and chromosomally intermediate between ''A. azarae boliviensis'' and ''A. infulatus'' | journal = Primates | volume = 34 | pages = 197–204 | doi = 10.1007/BF02381390 | issue = 2| s2cid = 38394366 }}</ref> Two [[extinct]] species of Aotidae are known from the [[fossil]] record: ''[[Aotus dindensis]]'' and ''[[Tremacebus harringtoni]]''.<ref name=Silvestro>{{Cite journal |last=Silvestro |first=Daniele |last2=Tejedor |first2=Marcelo F |last3=Serrano-Serrano |first3=Martha L |last4=Loiseau |first4=Oriane |last5=Rossier |first5=Victor |last6=Rolland |first6=Jonathan |last7=Zizka |first7=Alexander |last8=Höhna |first8=Sebastian |last9=Antonelli |first9=Alexandre |last10=Salamin |first10=Nicolas |date=2019-01-01 |title=Early Arrival and Climatically-Linked Geographic Expansion of New World Monkeys from Tiny African Ancestors |journal=Systematic Biology |volume=68 |issue=1 |pages=78–92 |doi=10.1093/sysbio/syy046 |issn=1063-5157 |pmc=6292484 |pmid=29931325}}</ref>

===Classification===
[[File:Stavenn Aotus trivirgatus 00.jpg|thumb|Three-striped night monkey]]
{{see also|List of platyrrhines}}
'''Family Aotidae'''
* Genus ''Aotus''
** ''Aotus lemurinus'' (gray-necked) group:
*** [[Gray-bellied night monkey]], ''Aotus lemurinus''
*** [[Panamanian night monkey]], ''Aotus zonalis''
*** [[Gray-handed night monkey]], ''Aotus griseimembra''
*** [[Hernández-Camacho's night monkey]], ''Aotus jorgehernandezi''
*** [[Brumback's night monkey]], ''Aotus brumbacki''
*** [[Three-striped night monkey]], ''Aotus trivirgatus''
*** [[Spix's night monkey]], ''Aotus vociferans''
** ''Aotus azarae'' (red-necked) group:
*** [[Azara's night monkey]], ''Aotus azarae''
*** [[Peruvian night monkey]], ''Aotus miconax''
*** [[Nancy Ma's night monkey]], ''Aotus nancymaae''
*** [[Black-headed night monkey]], ''Aotus nigriceps''
** Group ''[[Incertae sedis]]''
*** {{extinct}}''[[Aotus dindensis]]''
* Genus {{extinct}}''[[Tremacebus]]''
** {{extinct}}''Tremacebus harringtoni''

==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 reflective layer behind the retina possessed by many nocturnal animals.<ref name = "Schwab2002">{{cite journal
 | last1 = Schwab | first1 = I. R. | last2 = Yuen | first2 = C. K.
 | last3 = Buyukmihci | first3 = N. C. | last4 = Blankenship | first4 = T. N.
 | last5 = Fitzgerald | first5 = P. G. | title = Evolution of the tapetum
 | journal = Transactions of the American Ophthalmological Society
 | volume = 100 | pages = 187–200 | date = 2002 | pmc = 1358962 | pmid=12545693}}</ref> Other sources say they have a tapetum lucidum composed of [[collagen]] fibrils.<ref name="Ollivier2004">{{cite journal|last1=Ollivier|first1=F. J.|last2=Samuelson|first2=D. A.|last3=Brooks|first3=D. E.|last4=Lewis|first4=P. A.|last5=Kallberg|first5=M. E.|last6=Komaromy|first6=A. M.|title=Comparative morphology of the tapetum lucidum (among selected species)|journal=Veterinary Ophthalmology|volume=7|issue=1|date=2004-01-26|pages=11–22|doi=10.1111/j.1463-5224.2004.00318.x|pmid=14738502}}</ref> At any rate, night monkeys lack the tapetum lucidum composed of riboflavin crystals possessed by lemurs and other [[strepsirrhines]],<ref name="Ollivier2004" /> which is an indication that their nocturnality is a secondary adaption evolved from ancestrally 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]] at around {{Convert|1254|g|lb}}, and the lightest is [[Brumback's night monkey]], which weighs between {{Convert|455|and|875|g|lb}}. The male is slightly taller than the female, measuring {{Convert|346|and|341|mm|in}}, respectively.<ref name=Lang/>

==Ecology==
Night monkeys can be found in [[Panama]], [[Colombia]], [[Ecuador]], [[Peru]], [[Brazil]], [[Paraguay]], [[Argentina]], [[Bolivia]], and [[Venezuela]]. The species that live at higher elevations and colder latitudes tend to have thicker fur.<ref>{{Citation |last=Perea-Rodríguez |first=Juan Pablo |title=What Owl Monkeys (Aotus spp.) Tell Us About the Dynamics Between Thermo-Energetics and Organismal Biology |date=2023 |work=Owl Monkeys: Biology, Adaptive Radiation, and Behavioral Ecology of the Only Nocturnal Primate in the Americas |pages=301–321 |editor-last=Fernandez-Duque |editor-first=Eduardo |url=https://link.springer.com/chapter/10.1007/978-3-031-13555-2_10 |access-date=2025-03-28 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-031-13555-2_10 |isbn=978-3-031-13555-2 |last2=de la Iglesia |first2=Horacio |last3=Fernandez-Duque |first3=Eduardo|url-access=subscription }}</ref> Night monkeys can live in forests undisturbed by humans ([[primary forest]]) as well as in forests that are recovering from human logging efforts ([[secondary forest]]).<ref name=Lang>{{cite web|author=Cawthon Lang KA|date=2005-07-18|url=http://pin.primate.wisc.edu/factsheets/entry/owl_monkey/taxon|title=Primate Factsheets: Owl monkey (''Aotus'') Taxonomy, Morphology, & Ecology|access-date=2012-07-25}}</ref>

=== 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.<ref name="Ferndandez-Duque-2012">{{Cite journal|last=Ferndandez- Duque|first=E|date=2012|title=Owl Monkeys ''Aotus'' spp. in the wild and in captivity|journal=International Zoo Yearbook|volume=46|pages=80–94|doi=10.1111/j.1748-1090.2011.00156.x|hdl=11336/101658|hdl-access=free}}</ref> 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]] occurs in both flooded and unflooded tropical rainforest regions of Peru, preferring moist swamp and mountainous areas.<ref>{{Cite journal|last1=Carrillo-Bilbao|first1=Gabriel|last2=Fiore|first2=Anthony Di|last3=Fernandez-Duque|first3=Eduardo|date=2008-04-01|title=Behavior, Ecology, and Demography of ''Aotus vociferans'' in Yasuní National Park, Ecuador|journal=International Journal of Primatology|language=en|volume=29|issue=2|pages=421–431|doi=10.1007/s10764-008-9244-y|s2cid=10756899|issn=1573-8604|hdl=11336/104477|hdl-access=free}}</ref> This species has been observed nesting in regions of the Andes<ref name="Shanee-2015">{{Cite journal|last1=Shanee|first1=Sam|last2=Allgas|first2=Nestor|last3=Shanee|first3=Noga|last4=Campbell|first4=Nicola|date=2015-03-26|title=Distribution, ecological niche modelling and conservation assessment of the Peruvian Night Monkey (Mammalia: Primates: Aotidae: ''Aotus miconax'' Thomas, 1927) in northeastern Peru, with notes on the distributions of ''Aotus'' spp.|journal=Journal of Threatened Taxa|volume=7|issue=3|pages=6947–6964|doi=10.11609/jott.o4184.6947-64|issn=0974-7893|doi-access=free}}</ref> and has recently been introduced to Colombia, likely as a result of post-research release into the community.<ref name="Svensson-2016">{{Cite journal|last1=Svensson|first1=Magdalena S.|last2=Shanee|first2=Sam|last3=Shanee|first3=Noga|last4=Bannister|first4=Flavia B.|last5=Cervera|first5=Laura|last6=Donati|first6=Giuseppe|last7=Huck|first7=Maren|last8=Jerusalinsky|first8=Leandro|last9=Juarez|first9=Cecilia P.|date=2016|title=Disappearing in the Night: An Overview on Trade and Legislation of Night Monkeys in South and Central America|journal=Folia Primatologica|volume=87|issue=5|pages=332–348|doi=10.1159/000454803|pmid=28095375|s2cid=21924164|issn=0015-5713|url=http://sro.sussex.ac.uk/66059/1/Svensson%20et%20al%202016_revised.pdf}}</ref> The [[black-headed night monkey]] is also found mainly in the Peruvian Amazon (central and upper Amazon), however its range extends throughout Brazil and Bolivia<ref>{{Cite journal|last=Anderson|first=S|date=1997|title=Mammals of Bolivia, taxonomy and distribution|journal=Bulletin of the American Museum of Natural History|volume=231}}</ref> to the base of the Andes mountain chain.<ref name="Hershkovitz-1983">{{Cite journal|last=Hershkovitz|first=Philip|date=1983|title=Two new species of night monkeys, genus ''Aotus'' (Cebidae, platyrrhini): A preliminary report on ''Aotus'' taxonomy|journal=American Journal of Primatology|volume=4|issue=3|pages=209–243|doi=10.1002/ajp.1350040302|pmid=31991954|s2cid=84562795|issn=0275-2565}}</ref> 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]], like Nancy Ma's night monkey, is endemic to the Peruvian Andes however it is found at a higher elevation, approximately {{Convert|800|-|2400|m|ft}} above sea level and therefore exploits different niches of this habitat.<ref name="Hershkovitz-1983" /> The distribution of ''A. azare'', extends further towards the Atlantic Ocean, spanning Argentina, Bolivia and the drier, south western regions of Paraguay,<ref>{{Cite journal|last1=Fernandez-Duque|first1=Eduardo|last2=Di Fiore|first2=Anthony|last3=Carrillo-Bilbao|first3=Gabriel|date=April 2008|title=Behavior, Ecology, and Demography of ''Aotus vociferans'' in Yasuní National Park, Ecuador|journal=International Journal of Primatology|volume=29|issue=2|pages=421–431|doi=10.1007/s10764-008-9244-y|s2cid=10756899|issn=0164-0291|hdl=11336/104477|hdl-access=free}}</ref> 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.<ref name="Aquino-1986">{{Cite journal|last1=Aquino|first1=Rolando|last2=Encarnación|first2=Filomeno|date=1986|title=Characteristics and use of sleeping sites in ''Aotus'' (Cebidae: Primates) in the Amazon lowlands of Peru|journal=American Journal of Primatology|volume=11|issue=4|pages=319–331|doi=10.1002/ajp.1350110403|pmid=31979438|s2cid=84650076|issn=0275-2565}}</ref> 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.<ref name="Aquino-1986" /> 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.<ref name="Aquino-1986" /> Night monkeys represent a territorial species, territories are defended by conspecifics through the use of threatening and agonistic behaviours.<ref>{{Cite journal|last=Bates|first=Brian C.|date=September 1970|title=Territorial behavior in primates: A review of recent field studies|journal=Primates|volume=11|issue=3|pages=271–284|doi=10.1007/bf01793893|s2cid=46168799|issn=0032-8332}}</ref> 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.<ref name="Ferndandez-Duque-2012" />

=== Diet ===
Night monkeys are primarily [[frugivorous]], as fruits are easily distinguished through the use of olfactory cues,<ref name="Fernández-Duque-2010"/> but leaf and insect consumption has also been observed in the cathemeral night monkey species ''A. azare''.<ref name="Ferndandez-Duque-2012" /> 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.<ref name="Wolovich-2007">{{Cite journal|last1=Wolovich|first1=Christy Kaitlyn|last2=Evans|first2=Sian|date=December 2007|title=Sociosexual Behavior and Chemical Communication of ''Aotus nancymaae''|journal=International Journal of Primatology|volume=28|issue=6|pages=1299–1313|doi=10.1007/s10764-007-9228-3|s2cid=38645815|issn=0164-0291}}</ref> 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.<ref name="Wolovich-2007" /> 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.<ref name="Ferndandez-Duque-2012" />

=== Reproduction ===
In night monkeys, mating occurs infrequently, however females are fertile year-round, with reproductive cycles range from 13 to 25 days.<ref name="Dixson-1982">{{Cite journal|last=Dixson|first=A. F.|date=January 1982|title=Some observations on the reproductive physiology and behaviour of the Owl monkey in captivity|journal=International Zoo Yearbook|volume=22|issue=1|pages=115–119|doi=10.1111/j.1748-1090.1982.tb02017.x|issn=0074-9664}}</ref> 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-dependent, with one offspring being produced per year; however, in studies conducted in captivity, twins were observed.<ref name="Dixson-1982" /> Night monkeys reach puberty at a relatively young age, between 7 and 11 months, and most species attain full sexual maturity by the time they reach 2 years of age. ''A. azare'' represents an exception reaching sexual maturity by the age of 4.<ref name="Dixson-1982" />

==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]], ''Aotus azarae azarae'', which is [[cathemeral]]).<ref name=Lang/> 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&nbsp;Hz.<ref>{{cite journal | author = Moynihan, M. | title = Some behavior patterns of platyrrhine monkeys. I. The night monkey (''Aotus trivirgatus'') | journal = Smithsonian Miscellaneous Collections | year = 1964 | volume = 146 | issue = 5 | pages = 1–84}}</ref> Unusual among the New World monkeys, they are [[monochromat]]s, 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.<ref>{{cite journal | author = Jacobs, G. H. | author2 = Deegan, J. F. | author3 = Neitz, J. | author4 = Crognale, M. A. | year = 1993 | title = Photopigments and colour vision in the nocturnal monkey, ''Aotus'' | journal = Vision Research | volume = 33 | pages = 1773–1783 | doi = 10.1016/0042-6989(93)90168-V | pmid = 8266633 | issue = 13| citeseerx = 10.1.1.568.1560 | s2cid = 3745725 }}</ref> Night monkeys live in family groups consisting of a mated pair and their immature offspring. Family groups defend [[territory (animal)|territories]] by vocal calls and [[scent marking]].

The night monkey is socially monogamous, and all night monkeys form [[pair bond]]s.<ref>{{Cite web |last=Cummings |first=Mike |date=November 13, 2023 |title=Good partners and great dads: insights into the world of owl monkeys |url=https://news.yale.edu/2023/11/13/good-partners-and-great-dads-insights-world-owl-monkeys |access-date=August 8, 2024 |website=Yale News}}</ref> 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.<ref name="Fernandez-Duque2008">{{Cite journal | last1 = Fernandez-Duque | first1 = E. | title = Natal dispersal in monogamous owl monkeys (''Aotus azarai'') of the Argentinean Chaco | doi = 10.1163/156853908X397925 | journal = Behaviour | volume = 146 | issue = 4 | pages = 583–606 | year = 2009 | hdl = 11336/104367 | url = http://www.sas.upenn.edu/~eduardof/Publications/Fernandez-Duque%202009%20Natal%20Dispersal.pdf| citeseerx = 10.1.1.533.3310 }}</ref>

=== Nocturnality ===
The family Aotidae is the only family of nocturnal species within the suborder [[Simian|Anthropoidea]]. Whereas other divisions of primates, including [[Strepsirrhini]] and [[Tarsier|Tarsiidae]], include many nocturnal and cathemeral species, 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.<ref name="Ankel-Simons-2008">{{Cite journal|last1=Ankel-Simons|first1=F.|last2=Rasmussen|first2=D.T.|date=2008|title=Diurnality, nocturnality, and the evolution of primate visual systems|journal=American Journal of Physical Anthropology|volume=137|issue=S47|pages=100–117|doi=10.1002/ajpa.20957|pmid=19003895|issn=0002-9483|doi-access=free}}</ref> &nbsp;The presence of nocturnal behavior in Aotidae therefore exemplifies a derived trait; an evolutionary adaptation that conferred greater fitness advantages onto the night monkey.<ref name="Ankel-Simons-2008" /> &nbsp;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.<ref name="Wright-1989">{{Cite journal|last=Wright|first=Patricia C.|date=November 1989|title=The nocturnal primate niche in the New World|journal=Journal of Human Evolution|volume=18|issue=7|pages=635–658|doi=10.1016/0047-2484(89)90098-5|bibcode=1989JHumE..18..635W |issn=0047-2484}}</ref> 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.<ref name="Wright-1989" /> 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.<ref name="Ankel-Simons-2008" /> 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.<ref name="Fernández-Duque-2010">{{Cite journal|last1=Fernández-Duque|first1=Eduardo|last2=de la Iglesia|first2=Horacio|last3=Erkert|first3=Hans G.|date=2010-09-03|title=Moonstruck Primates: Owl Monkeys (''Aotus'') Need Moonlight for Nocturnal Activity in Their Natural Environment|journal=PLOS ONE|volume=5|issue=9|article-number=e12572|doi=10.1371/journal.pone.0012572|pmid=20838447|pmc=2933241|issn=1932-6203|bibcode=2010PLoSO...512572F|doi-access=free}}</ref> To begin, resting during the day allows for decreased interaction with diurnal predators. Members of the family Aotidae apply predation avoidance in choosing strategic covered nest sites in trees.<ref name="Savagian-2017">{{Cite journal|last1=Savagian|first1=Amanda|last2=Fernandez-Duque|first2=Eduardo|date=2017-01-04|title=Do Predators and Thermoregulation Influence Choice of Sleeping Sites and Sleeping Behavior in Azara's Owl Monkeys (''Aotus azarae azarae'') in Northern Argentina?|journal=International Journal of Primatology|volume=38|issue=1|pages=80–99|doi=10.1007/s10764-016-9946-5|s2cid=9881118|issn=0164-0291}}</ref> 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.<ref name="Fernández-Duque-2010" /><ref name="Aquino-1986" /> 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.<ref name="Fernández-Duque-2010" />

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.<ref name="Savagian-2017" /> 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.<ref name="Savagian-2017" /> 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.<ref name="Savagian-2017" /> 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.<ref name="Savagian-2017" />

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.<ref name="Fernandez-Duque-2003">{{Cite journal|last=Fernandez-Duque|first=Eduardo|date=2003-09-01|title=Influences of moonlight, ambient temperature, and food availability on the diurnal and nocturnal activity of owl monkeys (''Aotus azarai'')|journal=Behavioral Ecology and Sociobiology|volume=54|issue=5|pages=431–440|doi=10.1007/s00265-003-0637-9|bibcode=2003BEcoS..54..431F |s2cid=32421271|issn=0340-5443|hdl=11336/50695|hdl-access=free}}</ref> 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.<ref name="Fernandez-Duque-2003" /> Therefore, the lunar cycle has a significant influence on the foraging and a nocturnal behaviors of night monkey species.<ref name="Fernandez-Duque-2003" />

=== 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.<ref name="Fernandez-Duque-2012">{{Cite journal|last=Fernandez-Duque|first=E.|date=January 2012|title=Owl monkeys ''Aotus'' spp in the wild and in captivity|journal=International Zoo Yearbook|volume=46|issue=1|pages=80–94|doi=10.1111/j.1748-1090.2011.00156.x|issn=0074-9664|hdl=11336/101658|hdl-access=free}}</ref> 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.<ref name="Wartmann-2014">{{Cite journal|last1=Wartmann|first1=Flurina M.|last2=Juárez|first2=Cecilia P.|last3=Fernandez-Duque|first3=Eduardo|date=2014-07-04|title=Erratum to: Size, Site Fidelity, and Overlap of Home Ranges and Core Areas in the Socially Monogamous Owl Monkey (''Aotus azarae'') of Northern Argentina|journal=International Journal of Primatology|volume=35|issue=5|page=940|doi=10.1007/s10764-014-9787-z|issn=0164-0291|doi-access=free}}</ref>&nbsp; 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.<ref>{{Cite journal|last=Fernandez-Duque|first=Eduardo|date=March 2016|title=Social monogamy in wild owl monkeys ( Aotus azarae ) of Argentina: the potential influences of resource distribution and ranging patterns: Monogamy in Owl Monkeys|journal=American Journal of Primatology|language=en|volume=78|issue=3|pages=355–371|doi=10.1002/ajp.22397|pmc=5398412|pmid=25931263}}</ref> Night monkeys form bonded pairs and the energy expenditure of protecting a mate is reduced.<ref name="Wartmann-2014" /> 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.<ref name="Fernandez-Duque-2015">{{Cite journal|last=Fernandez- Duque|first=E|date=2015|title=Love in the time of Monkeys|journal=Natural History|volume=122|jstor=}}</ref> 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.<ref name="Fernandez-Duque-2015" />

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.<ref name="Fernandez-Duque-2012" /> In addition to aiding in child care, males will support females during lactation through sharing their foraged food with lactating females.<ref name="Wolovich-2008">{{Cite journal|last1=Wolovich|first1=Christy K.|last2=Evans|first2=Sian|last3=French|first3=Jeffrey A.|date=March 2008|title=Dads do not pay for sex but do buy the milk: food sharing and reproduction in owl monkeys (''Aotus'' spp.)|journal=Animal Behaviour|volume=75|issue=3|pages=1155–1163|doi=10.1016/j.anbehav.2007.09.023|s2cid=36121485|issn=0003-3472}}</ref> 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.<ref name="Wolovich-2008" /> 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.<ref name="Wolovich-2008" />

=== 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.<ref name="Wolovich-2007" /> 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.<ref name="Bolen-1997">{{Cite journal|last1=Bolen|first1=Rosina H.|last2=Green|first2=Steven M.|date=1997|title=Use of olfactory cues in foraging by owl monkeys (''Aotus nancymai'') and capuchin monkeys (Cebus apella).|journal=Journal of Comparative Psychology|volume=111|issue=2|pages=152–158|doi=10.1037/0735-7036.111.2.152|pmid=9170280|issn=1939-2087}}</ref> 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.<ref name="Bolen-1997" /> 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.<ref name="Wolovich-2007" />

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.<ref name="Bolen-1997" /> 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.<ref name="Bolen-1997" /> 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.<ref name="Wolovich-2007" /> 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.<ref name="Wolovich-2007" /> 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.<ref name="Wolovich-2007" /> 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.<ref name="Wolovich-2007" /> Therefore, night monkey olfactory communication, as a sexually dimorphic trait conferring increased reproductive success, is a result of [[sexual selection]]. This trait demonstrates sexual dimorphism, as males have larger subcaudal scent glands compared to female counterparts and sex differences have been recorded in the glandular secretions of each sex.<ref name="Spence-Aizenberg-2018">{{Cite journal|last1=Spence-Aizenberg|first1=Andrea|last2=Williams|first2=Lawrence E.|last3=Fernandez-Duque|first3=Eduardo|date=2018-05-02|title=Are olfactory traits in a pair-bonded primate under sexual selection? An evaluation of sexual dimorphism in ''Aotus nancymaae''|journal=American Journal of Physical Anthropology|volume=166|issue=4|pages=884–894|doi=10.1002/ajpa.23487|pmid=29719049|issn=0002-9483|doi-access=free}}</ref> 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.<ref name="Spence-Aizenberg-2018" />

== Conservation ==
According to the IUCN (the [[International Union for Conservation of Nature]]), the [[Peruvian night monkey]] is classified an [[Endangered species]], four species are [[Vulnerable species|Vulnerable]], four are [[Least-concern species]], and two are data deficient. Most night monkey species are threatened by varying levels of habitat loss throughout their range, caused by [[agricultural expansion]], 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]] has been destroyed or degraded by human activities.<ref name="Shanee-2015" /> 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.<ref name="Shanee-2015" /> Studies have already been conducted into the feasibility of agroforestry; plantations which simultaneously support local species biodiversity.<ref name="Guzmán-2016">{{Cite journal|last1=Guzmán|first1=Adriana|last2=Link|first2=Andrés|last3=Castillo|first3=Jaime A.|last4=Botero|first4=Jorge E.|date=January 2016|title=Agroecosystems and primate conservation: Shade coffee as potential habitat for the conservation of Andean night monkeys in the northern Andes|journal=Agriculture, Ecosystems & Environment|volume=215|pages=57–67|doi=10.1016/j.agee.2015.09.002|bibcode=2016AgEE..215...57G |issn=0167-8809}}</ref> 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.<ref name="Guzmán-2016" /> 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.<ref name="Guzmán-2016" />

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).&nbsp; 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<ref name="Svensson-2016" /> 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]], like human beings, are susceptible to infection by the ''[[Plasmodium falciparum]]'' parasite responsible for malaria.<ref>{{cite book | editor = Baer, J.F. |editor2=Weller, R.E. |editor3=Kakoma, I. | title = ''Aotus'': The Owl Monkey | location = San Diego | year = 1994 | isbn = 978-0-12-072405-5 | publisher = Academic Press}}</ref> This trait caused them to be recommended by the World Health Organization as test subjects in the development of malaria vaccines.<ref>{{Cite journal|last1=Nino-Vasquez|first1=J. Javier|last2=Vogel|first2=Denise|last3=Rodriguez|first3=Raul|last4=Moreno|first4=Alberto|last5=Patarroyo|first5=Manuel Elkin|last6=Pluschke|first6=Gerd|last7=Daubenberger|first7=Claudia A.|date=2000-03-03|title=Sequence and diversity of DRB genes of ''Aotus nancymaae'', a primate model for human malaria parasites|journal=Immunogenetics|volume=51|issue=3|pages=219–230|doi=10.1007/s002510050035|pmid=10752632|s2cid=24133733|issn=0093-7711}}</ref> 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.<ref>{{Cite journal|last=Bunyard|first=P|date=2008|title=Monkey Business|journal=Ecologist|volume=38|pages=48–51|via=Ebscohost}}</ref>

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.<ref name="Juarez-2010">{{Cite journal|last1=Juarez|first1=Cecilia Paola|last2=Rotundo|first2=Marcelo Alejandro|last3=Berg|first3=Wendy|last4=Fernández-Duque|first4=Eduardo|date=2010-10-07|title=Costs and Benefits of Radio-collaring on the Behavior, Demography, and Conservation of Owl Monkeys (''Aotus azarai'') in Formosa, Argentina|journal=International Journal of Primatology|volume=32|issue=1|pages=69–82|doi=10.1007/s10764-010-9437-z|s2cid=24198124|issn=0164-0291|hdl=11336/27058|hdl-access=free}}</ref> 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.<ref name="Juarez-2010" />  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.<ref name="Juarez-2010" />

==References==
{{Reflist}}

==External links==
* [http://pin.primate.wisc.edu/factsheets/entry/owl_monkey Primate Info Net ''Aotus'' Factsheet]

{{Primates}}
{{Aotidae nav}}
{{Haplorhini|S.}}
{{Taxonbar|from1=Q15407957|from2=Q469636}}

[[Category:Night monkeys| ]]
[[Category:Taxa named by Johann Karl Wilhelm Illiger]]