Panamanian Night Monkey, Aotus zonalis
PANAMANIAN NIGHT MONKEY
Geographic Distribution and Habitat
Panamanian night monkeys—also known as Chocoan night monkeys or Cocoan owl monkeys—live in the lowlands of Panama and in the western or Chocó region of Colombia. There have also been reports of their incidence on the Caribbean coast of Costa Rica.
Panamanian night monkeys primarily live in mature and secondary forests. These forests are typically very humid with altitudes up to 3,280 feet (1,000 m) above sea level. The Panamanian night monkey can also be found in altered forests (forests altered by human activities), dry forests, forest plantations, coffee crops, and mangroves.
The taxonomy of the Aotus genus, the taxon of night monkeys, is still somewhat unresolved. Until 1983, all night monkeys were considered to be one of two night monkey species: Aotus lemurinus or Aotus azarea. These two are now considered distinct species in their own right. A. lemurinus is the Colombian night monkey and A. azaraea is the Azara’s night monkey. The Panamanian night monkey (A. zonalis), the subject of this profile, was also recognized as a distinct species at that time, along with six to eight other night monkey species (including those already mentioned). These distinctions were reaffirmed in 2007.
Size, Weight, and Lifespan
The Panamanian night monkey is a relatively small monkey, with a head-to-body length measuring 12–13 inches (30.5–33 cm). The tails adds about another 12 in (30 cm) to their small bodies. Males and females are similar in size, with males weighing approximately 1.9 pounds (0.88 kg) and females weighing about 2 pounds (.91 kg).
Night monkeys, on average, live 11–14 years in the wild and up to 20 years in captivity.
The Panamanian night monkey has large brown eyes, which, unlike many nocturnal animals, lack a tapetum lucidum. The tapetum lucidum is a layer of tissue in the eye that lies behind the retina, reflects light back through the retina, and contributes to night vision. This is what gives nocturnal animals the typical “eyeshine,” which night monkeys lack. Night monkeys’ night vision benefits from the retina containing a greater number of rods (responsible for vision at low light levels) than cones (responsible for vision at higher light levels). Their vision is also monochromatic, which means that they can only see in one color—typically shades of gray.
Although the name Aotus means “without ears,” night monkeys do, indeed, have tiny hard-to-see ears surrounded by tufts of hair. Their hair is gray-brown to reddish-brown with yellowish belly hair. The back of their hands and feet have dark brown or black hair. The thickness and length of their coat depend on the altitude at which they live. Those that live in higher altitudes have thicker and shaggier coats than those that live at sea level.
Unique facial markings are common in night monkeys, including the Panamanian night monkey. Black stripes can be found starting at the top of their heads to either side of their face and on the bridge of their nose.
Like many night monkeys, the tail can be relatively long compared to body size. Tails are nonprehensile (incapable of grasping objects) and help them balance during locomotion. They have long slender fingers and large digital pads on their hands and feet. Night monkeys possess a slightly opposable thumb, and often a compressed, claw-like grooming nail on the second digit of each foot.
Night monkeys are mostly frugivorous. When available they prefer small ripe fruit, which happens to be located high in tree crowns. They also enjoy flowers, nectar, leaves, and insects if fruit can’t be found. The availability of fruit varies across environments. Those that live in tropical forests eat more fruit than those that live in dry forests, who are more dependent on leaves.
At dawn and dusk, night monkeys may forage for insects. They mostly eat large locusts, moths, crickets, beetles, and spiders. Instead of searching in crevices or holes for these insects, night monkeys are experts at grabbing them as they fly through the air. Orthopterans, such as locusts and crickets, are mostly active during the night. They call loudly and create specific rhythms that expose their location, making them easier to find and capture in darkness.
Behavior and Lifestyle
Panamanian night monkeys are arboreal (tree-dwelling) and nocturnal, meaning they are active during the night, especially at dawn and dusk. During the day they sleep or rest inside of tree holes or in beds of leaves between branches. At night, they move quadrupedally (on all fours) through branches, running and jumping adeptly.
Night monkeys are sympatric with other species. They do not compete for resources with other animals within their range due to their alternating schedules. Usually other nocturnal animals, like bats, who forage alone or in pairs, do not pose a significant source of competition.
Night monkeys, like most monkeys, are endothermic, meaning they can produce their own heat. During the day they undergo a behavioral thermoregulation by resting so they can minimize their energy expenditure. During the hottest points of the day, night monkeys are resting and thus save energy.
Panamanian night monkeys are monochromatic; that is, they only see the world in shades of gray.
Night monkeys benefit from a nocturnal lifestyle as nighttime activity provides a degree of protection from the heat of the day, predators, and thermoregulation difficulties.
Panamanian night monkeys are one of a few species of monogamous monkeys. They live in small groups of between two to six individuals, consisting of a bonded adult pair, several young, and subadults. Groups are territorial and occupy specific regions that often overlap with other groups. Depending on the species and location, night monkeys occupy territories between 33 to 121 yards (30–110 m).
Both males and females disperse from their groups when they reach sexual maturity at about 2 years of age. Groups have unique social behaviors and rarely participate in social grooming. Most social behaviors are reflected in the manner in which they communicate with one another. They use hoots, whoops, and play as forms of socialization.
Moonlight is important for Panamanian night monkeys. When the moon is bright, they travel further than when the night sky is gloomy and gray. The bright moonlight, of course, makes it easier for them to see. Night monkeys have good memory of their foraging routes.
Panamanian night monkeys are vocal primates. At least nine calls are recognized, including distinct grunts, squeals, screams, moans, and trills. They have specialized throat patches that inflate and increase the volume and power of calls.
Not much is known about their territorial calls, but it is assumed that they emit calls to reinforce home range boundaries and intergroup relationships. They emit aggression calls and alarm calls when a direct conflict arises between two groups. These sound like low grunts and even hoots that increase in volume. Purr sounds or low grunts and hoots are often used between group members (adults and juveniles) to reinforce bonds or to alert desirable food sources. When infants are hungry they use high-pitched squeaking sounds.
Olfactory communication is also common among night monkeys. Males develop scent glands near their tail at about one year of age and use them to scent mark trees and branches. Urine washing, where males and females rub urine on their hands and feet, is also common.
Behavioral displays, like arched back displays, stiff legged jumping, and piloerection (hair-bristling to appear larger) have been noted.
Panamanian night monkeys are monogamous, only mating with one partner at a time. These monogamous pairs may mate for life. Females give birth to one infant per year and occasionally bear twins. Co-parenting is common. In fact, males carry, play with, and protect their young. The father carries the infant from the first or second day after birth up until about five months, handing the child over to the mother for feeding. The mother nurses the infant for about 7 months. At about one year of age, infants are independent.
Due to their primarily frugivorous diet, night monkeys contribute to the reproduction of plants through the fruits and seeds they eat. After digestion, they disperse the seeds through their feces.
The Panamanian night monkey is not well studied, nor are populations well assessed. As a result, the International Union for Conservation of Nature categorizes the species as Near Threatened (IUCN, 2020), meaning there is little to no information on this species’ population size and trends.
Some species are little-studied because they live in very remote regions and are difficult to access. Some live too high in trees for humans to observe. Studying Panamanian night monkeys in the wild can be challenging because of the nocturnal lifestyle, leading to a dearth of research into the species ecology and conservation.
In Panama, threats include legal and illegal deforestation, urbanization, mine projects, and agricultural activities that have reduced Panamanian forest cover by 40% since 1950 . There is evidence that this primate has disappeared from some of its original Panamanian distribution. Reasons for population decline are also linked to urbanization in the Panama Canal Watershed, illegal logging in Darien province, and massive loss of virgin vegetation at Donoso, Colon province, due to mine activity and extirpated populations for laboratory purposes. In Colombia, more studies are in need to better understand the actual conservation status, but threats are evident as biomedical studies are still operating, and they are hunted for pet trade, hunting and bushmeat.
The Panamanian night monkey occurs in a number of protected areas throughout Panama, Columbia, and Costa Rica. They are also 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.
More research is needed on the threats of this species—especially research on population size and distribution. When more information is known about a species, more policies can be enacted to protect them and their habitats. The best policies can be put into action when we understand their resilience to human impacts.
- Fernandez-Duque, E. 2007. “Aotinae”. In Campbell, C., Fuentes, A., MacKinnon, K., Panger, M., & Bearder, S. Primates in Perspective. pp. 139–150.
- Mittermeier, R.A., Rylands, A.B., Wilson, D.E. 2013. The Mammals of the World, Part 3: Primates. Barcelona: Lynx Edicions…
Written by Tara Covert, March 2020, Conservation status update May 2021