Panamanian Night Monkey, Aotus zonalis
PANAMANIAN NIGHT MONKEY
Aotus zonalis
Geographic Distribution and Habitat
The Panamanian night monkey (Aotus zonalis), also known as the Chocoan night monkey, is a nocturnal primate species native to Panama and the Chocó region of Colombia, which refers to the area of land located on the Pacific coast and the greater Chocó Biogeographic Region. Locally, they are referred to as “martejas”.
In Panama, night monkeys have a geographic range that extends into many territories, including Soberanía National Park, Camino de Cruces National Park, Chagres National Park, Portobelo National Park, and the Colon province. In Colombia, they occur between the Andes and the Rio Raposo in the west, to the Urabá region and the Rio Sinú in the east, and possibly to the upper San Jorge valley and the region of Puerto Valdivia in northern Antioquia. Interestingly, there are some reports of Panamanian night monkeys occurring on the coastal shorelines of Costa Rica, although more research is needed to prove the claim to be true.
Across their geographic distribution, Panamanian night monkeys have an upper elevation limit of about 1 mile (1,600 meters).
Year-round, temperatures in Panama and Colombia range between 70 to 90 degrees Fahrenheit (21 to 32 degrees Celsius). Both countries experience a rainy and dry season, but the specific times of year differ. In Panama, the dry season, or “summer”, lasts between mid-December to mid-April. In Colombia, the months slightly differ since summer is experienced between December and February, and then again between July to August. Comparatively, the rainy season, also known as “winter”, lasts from May to December in Panama. In Colombia, winter occurs between April and May, and then again between September and November.
The rainy season is the greenest time of year and is typically accompanied by warm mornings and heavy rainfall or rainstorms in the afternoon. Influenced by atmospheric patterns, geographic features, and oceanic conditions, rainfall can vary depending on whether the ecosystem is on the side of the Pacific Ocean or on the side of the Caribbean Sea. For example, on the Caribbean side, the average annual rainfall can vary between 59 to 140 inches (150 to 360 centimeters). On the Pacific side, the average annual rainfall usually fluctuates between 45 to 90 inches (110 to 230 centimeters).
Unfortunately, the taxonomy of the Panamanian night monkeys is somewhat perplexing. That being said, scientists and primatologists continue to conduct ongoing research for this species, collecting data to support their taxonomic claims or disprove others’.
Until 1994, scientists believed there to be only two species of night monkey north of the Amazon River: the northern night monkey (Aotus trivirgatus) and the Spix’s night monkey (Aotus vociferans). Interestingly, under this distinction, the Spix’s night monkey was believed to include all subspecies found in Peru, Colombia, Ecuador, and Panama, which included Brumback’s night monkey (Aotus brumbacki), the Colombian night monkey (Aotus lemurinus), the gray-handed night monkey (Aotus griseimembra), and the Panamanian night monkey (Aotus zonalis).
More recently, the categorization of these species varied; some scientists categorized them together, while others categorized them separately. However, in most circumstances, the form “zonalis” was considered the only night monkey of north-western Colombia and Panama, and was soon after given the common name: “Panamanian night monkey”.
Size, Weight, and Lifespan
Panamanian night monkeys are small, weighing roughly 1.5 to 2 pounds (680.4 to 907 grams). The average adult male weighs around 1.95 pounds (889 grams), and the average adult female weighs around 2.01 pounds (916 grams). Additionally, the average head-to-body length for an individual is about 12 to 13 inches (30.5 to 33.02 centimeters). Interestingly, as a sexually dimorphic species, females tend to be slightly larger and heavier than males. Sexual dimorphism describes the noticeable difference between males and females in terms of their physical, physiologic, and behavioral attributes. Their size is further increased by the tail length, which adds another 12 inches (30.5 centimeters) to their size.
Although the average lifespan of Panamanian night monkeys is unknown, night monkeys in general are estimated to live an average of 11 to 14 years in the wild.
Appearance
Panamanian night monkeys have dense, multi-colored fur that varies between shades of brown, cream, and black. Their unique coloration is perfect camouflage for their natural environment, and it allows them to easily blend in with their surroundings. Interestingly, Panamanian night monkeys also have yellow-toned underbellies, which act as a countershade in the dark. At night, when low-intensity light shines from above, such as from the moon or stars, a nocturnal animal’s underside remains cast in shadow. A lighter belly coloration reduces the contrast between the lit top and shadowed bottom, making the animal appear optically flat, which makes the animal less recognizable as a distinct, solid object. Visually confused, predators are therefore less likely to detect Panamanian night monkeys in the dark and prey on them.
Accenting their head and face, Panamanian night monkeys have three black stripes that extend from the tops of their heads down to their eyes. These stripes, which appear symmetrically in three columns, stop just above the area where the eyebrows would be. Because this particular area is colored white, the details create an illusion that portrays Panamanian night monkeys as always being surprised!
Panamanian night monkeys have large, saucer-like eyes that are honey-brown in color and appear orange when reflected by light. Unlike some other species, Panamanian night monkeys do not have “glowing eyes” at night. This is due to the lack of the reflective layer of tissue behind their retina called the “tapetum lucidum”. The retina is the light-sensitive tissue that lines the back of the eye and contains photoreceptor cells. Traditionally, the tapetum lucidum works by reflecting light back through the retina, amplifying the available light for an animal’s photoreceptors. Any light is then transformed and turned into electrical signaling, which is then sent to the brain through the optic nerve.
Panamanian night monkeys do not have color vision, seeing mostly in shades of gray, so they do not see the world in the same way as humans. In fact, because their vision is adapted for seeing in low-light conditions, they do not need to rely on color to differentiate objects. Instead, they depend more on characteristics like texture to differentiate objects.
Lastly, Panamanian night monkeys do not have prehensile tails, which are specialized tails that animals use to grasp or hold on to objects. In fact, to some, having a prehensile tail is comparable to having a fifth limb. Because Panamanian night monkeys do not have prehensile tails, this appendage is instead used as balance support. Furthermore, the non-prehensile tail of Panamanian night monkeys acts as a counterweight and helps maintain an individual’s stability as they climb trees and traverse the forest.
Diet
Panamanian night monkeys are frugivorous primates, with fruit making up 65% or more of their diet. They prefer eating small, soft, and ripe fruits that are typically found high in the forest canopy. Such fruits include Panama berries (Muntingia calabura), peach palm fruits (Bactris gasipaes), figs (Ficus), etc. Because these fruits are not available at all times of the year, the diet of a Panamanian night monkey is seasonally dependent. As a result, they traverse the forest and follow the “movable feast” of fruits, locating the plants in bloom. When fruit is scarce, they supplement their diet by consuming other food sources such as nectar, flowers, leaves, shoots, moths, beetles, spiders, etc.
In addition to having well-adapted eyesight for their nocturnal lifestyle, Panamanian night monkeys have an increased ability for hearing and smelling, which they rely on to locate food sources and navigate the forest in the dark. Their heightened sense of smell is used to detect the presence of invertebrate species, and their extraordinary hearing allows them to actively listen for the natural calls and rhythms of nocturnal insects. Combined, their abilities make them expertly trained hunters!
Behavior and Lifestyle
Panamanian night monkeys are arboreal, tree-dwelling primates, so they spend most of their lives in the rainforest’s trees. Given that they are four-limbed climbers and leapers, Panamanian night monkeys are very agile and acrobatic. At night, they socialize, search for food sources, and traverse the forest, traveling around 0.5 miles (805 meters) each night.
Panamanian night monkeys are nocturnal primates, which means they are specially adapted to thrive at nighttime or under the cover of darkness. Each day, individuals wake shortly after sunset and remain active until the early morning or sunrise. Peak nocturnal activity occurs around dawn and dusk, particularly when light levels are low and the dark shades of nighttime transition into the vibrant colors of the morning (or vice versa at night). Once the sun has fully risen, they find dark, secluded areas for sleep, including hollow trunks or spaces that have thick leaf or vine growth. These spaces not only provide cover from the sun, but they also provide shelter and safety from harsh weather conditions and predators.
Panamanian night monkeys share overlapping territories with other primates, but because of their nocturnal lifestyle, interactions and socializations are considered rare. The list of primates that share territory with Panamanian night monkeys includes: mantled howler monkeys (Alouatta palliata), Geoffroy’s spider monkeys (Ateles geoffroyi), white-faced capuchins (Cebus imitator), Panamanian squirrel monkeys (Saimiri oerstedii), Geoffroy’s tamarins (Saguinus geoffroyi), and brown spider monkeys (Ateles fusciceps).
Predatory threats to the Panamanian night monkey include jaguars (Panthera onca), ocelots (Leopardus pardalis), cougars (Puma concolor), harpy eagles (Harpia harpyja), ornate hawk-eagles (Spizaetus ornatus), and other large reptiles.
The scientific name of the Panamanian night monkey is “Aotus zonalis”. In Greek, the word “aotus” is a compilation of two words: the word “a” (meaning “without”) and “ot” (meaning “ear”). Together, the phrase translates to “without ear” or “earless” in English.
Although we know that Panamanian night monkeys have ears (as observed in the photos!), they are extremely small and not easily observable from a distance. Often, they are hidden under the animal’s dense fur, which is why some people believed that they didn’t have ears at all!
Panamanian night monkeys are socially monogamous animals, meaning they form strong, long-term partnerships with one individual of the opposite sex for the majority of their lives. Bonded adults mate and raise offspring together, and because their troop includes an additional offspring and a few juveniles, their overall family group is relatively small. They are also naturally territorial, so a closely-bonded troop is important, especially when it comes to defending their territory from other species. Both females and males participate in territory defense and actively disperse to protect their territory from outsiders.
Although uncommon, lone adults have been identified wandering through wild rainforests in northern Colombia. Upon closer inspection, researchers observed the individuals to be carrying out their daily lives and behaviors without trouble, even though they seemed not to have a designated social group.
Panamanian night monkeys are very communicative animals and use a variety of vocal, olfactory, and behavioral tactics to convey messages.
Vocal communication is the transfer of information using sound produced by the body, such as the voice, to convey messages and affect the behavior of the sender and receiver. Utilizing pitch, volume, and speed, Panamanian night monkeys produce around 9 different types of vocal patterns, including grunts, screams, trills, moans, etc. Each call serves various functions, from alarms to mating calls or signs of pleasure.
Olfactory communication is the process by which chemical signals, such as scents or odors, are used to transmit information from a sender to a receiver, triggering a behavioral or physiological response. Primates often use olfactory communication to recognize group or family members, choose genetically suitable mates, define territory, or obtain additional social information. Because they have an enhanced sense of smell, this is especially useful at night when locating one another. Females possess specialized scent glands on their chests, tails, and genitals, which they use to rub their scent onto surfaces within their environment. Comparatively, males have scent glands on their tails and chest that develop after about one year of age. They are also known to urine wash, which is where they rub urine onto their hands and feet for social communication, sexual signaling, navigation, and territory marking.
Lastly, they use their bodies to communicate, specifically through behavioral displays such as back arching, stiff-legged jumping, urinating, and defecating.
The gestation period from conception to birth is about 133 days, after which a mother gives birth to one infant (although twins are not uncommon). Newborns usually weigh between 0.19 and 0.25 pounds (3 and 4 ounces).
When it comes to childcare, males take over almost all caregiving responsibilities. From the first day of birth, unless the infant is actively nursing from the mother, males are responsible for carrying the infant and giving them constant, undivided attention. This care lasts around two months, or until the infant becomes self-sufficient and independent.
After around 2 to 3 years of age, Panamanian night monkeys reach sexual maturity, at which point they will leave their troop to find a mate and establish their own monogamous family.
As frugivores, Panamanian night monkeys are natural seed dispersers and play a large role when it comes to maintaining the health and wellness of their ecosystem. After feeding on fruits, night monkeys naturally disperse seeds by throwing or defecating the product. Because an individual does not stay in the same place for long periods of time, their movement scatters seeds throughout the forest. This allows new plants to grow away from the parent plant, preventing the competition between the parent plant and the offspring for resources like sunlight, water, and space.
Overall, a Panamanian night monkey’s seed dispersal helps maintain the biodiversity and health of the forest, because it allows plants to grow in places that they otherwise might never have. Not only does this benefit future generations of night monkeys, but it is also beneficial for all other animals who utilize the resources that the habitat naturally provides.
The International Union for Conservation of Nature lists the Panamanian night monkey as Near Threatened (IUCN, December 1, 2020), appearing on the IUCN Red List of Threatened Species.
According to the Red List, Panamanian night monkeys were previously listed as Data Deficient, but are now assessed as Near Threatened based on new studies conducted in Panama by Fundación Pro-Conservación de los Primates Panameños (FCPP), which confirm significant population declines in new areas where they were previously protected. In the 1990s, Panamanian night monkeys were considered by researchers to be the third most commonly traded night monkey, based on a study of illegal cross-border trading. These trades occurred frequently and at an unsustainable rate. Although things have slightly slowed down since then, widespread populations are still in recovery.
Today, threats to Panamanian night monkeys are well-reported. In Panama, threats include illegal and legal deforestation, urbanization, mine projects, and agricultural activities that have reduced the country’s forest cover by 40% since 1950. In Colombia, forests in less than 10% of its range have been converted to pastures and agriculture.
In general, more research is needed to accurately report the species’ population status, threats, and habitat vulnerabilities.
The Panamanian night monkey is listed in Appendix II of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival.
Panamanian night monkeys occur in many protected areas across Panama and Colombia. In Panama, the species occurs in Darién National Park, Chagres National Park, Canglón National Park, Portobelo National Park, etc. In Colombia, the species occurs in Ensenada de Utría Natural National Park, Farallones de Cali Natural National Park, Paramillo Natural National Park, Los Katios Natural National Park, etc.
Fundación Pro-Conservación de los Primates Panameños (FCPP) is currently leading research projects in fragmented and urban habitats throughout Panama. Their projects include habitat surveys in combination with local communities, informative talks, and offering educational merchandise and materials. Most importantly, conservationists are educating community members and countering the belief that Panamanian night monkeys are predators for chickens and that their nocturnal activity makes them inherently evil. Although these beliefs are false, for a long time, they were enough of a justification for humans to eliminate or abuse Panamanian night monkeys.
- Henkel S, Setchell JM. Group and kin recognition via olfactory cues in chimpanzees (Pan troglodytes). Proc Biol Sci. 2018 Oct 24;285(1889):20181527. doi: 10.1098/rspb.2018.1527. PMID: 30355708; PMCID: PMC6234885.
- Rowland HM, Cuthill IC, Harvey IF, Speed MP, Ruxton GD. Can’t tell the caterpillars from the trees: countershading enhances survival in a woodland. Proc Biol Sci. 2008 Nov 22;275(1651):2539-45. doi: 10.1098/rspb.2008.0812. PMID: 18700207; PMCID: PMC2605806.
- https://www.iucnredlist.org/species/39953/17922442
- https://animalia.bio/panamanian-night-monkey?taxonomy=889
- https://www.vacationtopanama.com/travel-guide/panama-seasons/
- https://neprimateconservancy.org/gray-handed-night-monkey/
- https://lemur.duke.edu/nocturnal/
- https://littlerockzoo.com/animals/animal-habitats/nocturnal-primates/
- https://striresearch.si.edu/rainforest/home/canopy/#:~:text=The%20air%20is%20very%20still,hopping%20around%20in%20the%20branches.
- https://www.nature.com/news/2007/070903/full/news070903-18.html#:~:text=Study%20helps%20to%20answer%20question,months%20in%20a%20captive%20environment.
- https://en.wikipedia.org/wiki/Night_monkey
- https://www.yalescientific.org/2025/03/love-is-in-the-air/#:~:text=Based%20on%20their%20observations%2C%20the,and%20pair%2Dliving%20social%20system.
- https://primate.wisc.edu/primate-info-net/pin-factsheets/pin-factsheet-owl-monkey/#:~:text=Adult%20females%20rarely%20play%20with%20their%20offspring%20(Wright%201981).&text=Because%20the%20primary%20social%20unit,%2DDuque%20&%20Huntington%202002).
Written by Brooklynne Mitchell-Arno, Aug 2025