PYGMY SLOW LORIS

Nycticebus pygmaeus

Geographic Distribution and Habitat

The pygmy slow loris, also called the pygmy loris or the lesser slow loris, is a small-bodied prosimian found in eastern Cambodia, Lao PDR, and east of the Mekong River in Vietnam, with rare sightings in southern China. They inhabit a wide range of forest types (rain forests, evergreen forests, and even bamboo plantations) with the criteria of abundant leaf cover. Pygmy slow lorises have inadvertently been (re-)introduced to many areas, so pinpointing their endemic or original geographical region can be problematic.

They are sympatric with the Bengal slow loris (Nycticebus bengalensis), meaning that they occur in the same geographical region but avoid competition by having non-overlapping diets and different canopy height preferences.

Pygmy slow loris range, IUCN 2020

TAXONOMY IN TRANSITION

The changes in the taxonomy of pygmy slow lorises have been recent and exciting! In 2022, a new genus name, Xanthonyctecebus, has been proposed for the pygmy slow lorisThe family Lorisidae has traditionally been divided into four genera or groups of loris species. Slow loris species (including the pygmy loris) belong to the genus Nycticebus, meaning “night monkey,” which refers to their nocturnal habit and monkey-like appearance. Researchers, and in particular loris expert Dr. Anna Nekaris, have noted the remarkable differences between slow loris species and the pygmy slow loris in the field. The variation between members of this genus was so stark that field biologists would sometimes be unable to correctly classify pictures of the same species from different geographical regions. This prompted investigations into comparing genetics, behaviors, and morphology of pygmy slow lorises and other slow lorises. And the results of these studies show, pygmy slow lorises, as an evolutionary group, split from other slow lorises 10.2 MYA, making pygmy slow lorises much older on the evolutionary timeline. Below are some other differences between pygmy slow lorises and other loris species that support the new genus proposal:

  • All pygmy slow lorises habitually have twins (which is rare in among lorises)
  • They have hairless ear-tips and seasonally their coat color changes with the loss of their dorsal stripe
  • They have a protruding premaxilla (upper jaw bones) and black nose
  • They tend to be more social, faster, and louder than other lorises.

Pygmy slow lorises were initially named so for their small size, however since then, the smaller Philippine slow loris (Nycticebus menagensis) has been recognized. Thus, size is a less unique feature for the pygmy slow loris, and, considering variations with other slow lorises, experts have suggested that the common name should be “pygmy loris.” The immediately recognizable feature of pygmy slow lorises is their gold-red color. “Xantho-” refers to the color yellow, so Xanthonycticebus (directly translated to mean yellow night monkey) is considered a more appropriate phenotypic description of the pygmy slow loris.

Size, Weight, and Lifespan

As their name suggests, pygmy slow lorises are diminutive, ranging between 0.8 and 1.8 lbs (0.4–0.8 kg). On average, adults weigh approximately 1.1 lbs (0.49 kg), although their weight can fluctuate substantially with the seasons. Adults measure around 7.7–9.1 inches (0.2–0.23 m) in length, excluding their (very short) tail.

Although the average lifespan of wild individuals is not well known, they can live to over 20 years in captivity.

Appearance

In most photographs of the pygmy slow-loris, you will notice its bright gold-red pelage and even more luminescent large eyes. Their eyes seem to glow in the dark due to the tapetum lucidum , a series of reflector cells that enhance low-light conditions for nocturnal vision. Pygmy slow lorises have distinct facial markings, especially around their large eyes and small rounded ears that are hairless at the tips. Like other members of the order Strepsirrhini, their perpetually moist noses help them detect smells.

Pygmy slow lorises’ appearance can change when they develop a dorsal crest (raised, dark patch of fur running down the length of their back) and a silvery frost to the edges of their fur. The reason for this change is still a subject for research, but many have noted a seasonality to the pelage color variation. Some researchers have noted that the dorsal crest and frosted edges appear during the winter season in Vietnam (November–February). This suggests the change may be a camouflage and insulation adaption to their changing environment where, in low-rainfall winters, leaves fall. The darker fur matches better with the tree bark thus helping the pygmy lorises escape detection by predators. The darker fur can also be thicker and helps absorb more light energy, making thermoregulation more efficient during the winter.

Pygmy lorises spend much of their time clinging comfortably to trees for long periods of time. They maintain this posture with forelimbs and hind limbs that are of a similar size, and a very short tail. To maintain this grip, their arms and legs have a network of blood vessels, called rete mirabile, to flush the muscles with fresh blood. Hand and feet shape, with reduced second digits, enables comfortable quadrupedal movement through the canopy.

Similar to other prosimians, they have incisors that form a tooth-comb, which is used for grooming and foraging.

Male and female pygmy slow lorises have a very similar appearance and do not seem to display any sexual dimorphism.

Photo credit: David Haring/Duke Lemur Center/Creative Commons

What Does It Mean?

Estrus:
A recurring period of sexual receptivity and fertility in many female mammals.

Exudate:
A substance, such as gum, sap, or resin, which flows from the vascular system of a plant.

MYA: 
“Million years ago,” a science-related unit of time.

Pelage: 
The fur, hair, or wool of a mammal.

Prosimians:
The most primitive of the primates. “Prosimian” means pre-monkey. The living (extant) prosimians are in the suborder Prosimii, which includes four families of lemurs, the bushbabies (galagos), lorises and pottos, and the tarsiers.

Olfactory communication:
Communication between individuals that uses the sense of smell. In primates, scents used in olfactory communication are usually produced from urine, feces, or secretions from skin glands.

Sexual dimorphism:
Distinct difference in size or appearance between the sexes of an animal in addition to difference between the reproductive organs themselves.

Slash and burn agriculture:
A method of unsustainable farming where farmers clear land by cutting and burning flora in order to create an empty field—a “swidden”—for cultivation. Such practices are detrimental to local ecosystems.

Tooth-comb:
The incisors on the lower front jaw of some animals are grouped as if to form a comb. The tooth-comb is used by these animals to groom and clean their fur or hair.

Torpor:
A sleep-like state in which the body decreases physiological activity.

Visit the Glossary for more definitions

Diet

In the wild, around 60% of a pygmy slow loris’s diet consists of gum, saps, and nectar, and the remaining 40% consists of insects. However, it is likely that other plant and animal matter may make their way into their diet.

Due to their dependency on gums and saps, pygmy slow lorises are referred to as exudativores, “animals that feed on exudates.” Pygmy slow lorises bite through the bark of a tree to start the flow of sap. This gouging behavior is done using their modified teeth—their canines and incisors form a tooth comb and premolars form tusks. The sap that emerges from the tree hardens and is collected by the loris’s long tongue.

Behavior and Lifestyle

Pygmy slow lorises are arboreal and nocturnal, spending most of their lives in the tree canopy. As nocturnal foragers, they can spend up to 19 hours sleeping each day and tend to sleep curled up in a ball in the hollows of trees or on branches. They have a very strong grip and can hang from branches by their hind limbs for long periods. They tend to move along branches on all four limbs and rarely jump. 

During winter, they can become inactive for extended periods of time, slipping into torpor in order to save energy when food is less available.

Brachial glands on their upper arms produce a secretion that, when mixed with saliva, becomes toxic. When pygmy slow lorises are threatened, they stretch out their arms to activate the flow of the secretion and lick the brachial gland to mix their saliva with it, transferring the secretion into their mouths, and making their bite toxic. This makes the pygmy slow loris one of the very few species of venomous primates, with a bite that can incapacitate potential predators, which might include pythons, eagles, and, of course, humans.

Daily Life and Group Dynamics

In the wild, pygmy slow lorises seem to lead a mostly solitary lifestyle. Males and females do not appear to accompany each other when not breeding and they do not live in groups like many other primates. Home ranges of males can be large, though sleeping sites and territories are smaller. The territory of a male may overlap with that of several females. Males rarely share a territory with one another.

Fun Facts

Recent taxonomy changes have proposed that the pygmy slow loris be placed in its own genus, Xanthonycticebus.

They are one of the few primates that have a venomous bite, produced by mixing their saliva with secretions from their brachial glands. 

Using their super-strong grip and a special network of blood vessels in their arms and legs, they can hang from branches for hours at a time.

They are classified as exudativores, animals that feed on saps, nectar, and gums from plants.

Critical threats include habitat loss, their use in traditional medicine, and the illegal pet trade.

Communication

Despite their large eyes, visual communication seems to play a lesser role in social communication in pygmy slow lorises. Given their environment of dense tree canopy, their visual landscape is limited. Olfactory senses are the most developed sense for pygmy slow lorises as both sexes use urine and glandular secretions to mark their environment. Male pygmy slow loris will mark over urine marks of males and females with his own urine. They also produce scent from their brachial glands, but the role of this in communication is less understood.

Vocalizations of the pygmy slow loris are not well documented, although some types of calls have been identified including a hiss to ward off potential predators, a short whistle made by estrus females, and contact calls between mothers and infants that consist of chirps, clicks, and squeaks.

Reproduction and Family

Reproduction is strictly seasonal, with estrus occurring between July and October every year. A female only has a window of 4–5 days when she is fertile and swelling of sexual organs is seen during this time. Following mating, and after a gestation period of 6 months, females give birth between January and March. In the wild, twins are commonly born. In captivity, triplets and quadruplets have also been recorded.

When infants are very young they cling to their mothers’ bellies. From their first week of life, infant slow pygmy lorises are left alone, “parked” on branches while their mothers forage for food. From their second week, however, they start to follow their mother as she leaves to forage. Infants become weaned at approximately 133 days. Females reach sexual maturity sometime between 9 and 16 months, whereas males do not reach sexual maturity until around 18–20 months.

A male’s territory can contain multiple females. A male will probably mate with several different females during the mating season.

Photo credit: David Haring/Duke Lemur Center/Creative Commons

Ecological Role

The impact of the pygmy slow loris upon its environment is not yet well understood. One study of pygmy marmosets (Cebuella pygmae), a Latin American exudativore, showed that higher gouging rates and consumption of exudates stimulated the production of more exudates by the tree. Exudates help trees fight off infections, particularly by fungus species. So, one theory is that exudativores can benefit tree health by helping them stave off fatal infections. Since Pygmy lorises also consume insects they help maintain balance and control the population of insects that can reproduce in large numbers. Additionally, sometimes pygmy slow lorises can eat fruit as part of their diet, it is likely that they may play a role in seed dispersal.

Conservation Status and Threats

The pygmy slow loris is classified as Endangered by the International Union for Conservation of Nature (IUCN, 2015), appearing on the IUCN Red List of Threatened Species. 

The species is suspected to have undergone a decline of more than 50% over the last three generations (24 years, given a generation length of 8 years). It is suspected that the population will continue to decline by at least 50% over the next 24 years. Like most wildlife, habitat loss is a major reason for the population decline. Unfortunately, the cuteness factor of the pygmy slow loris has made it popular in the pet trade industry. Additionally, traditional medicine and bush meat markets also contribute to the killing of pygmy slow lorises. 

Human encroachment into the pygmy slow loris habitat through the development of settlements and agriculture (in particular rice and corn plantations that require deforestation) has drastically reduced their habitat and food sources. Slash and burn agriculture has resulted in the eradication of the pygmy slow loris from large areas. Habitat degradation of the pygmy slow loris’s home has been occurring for decades. During the Vietnam War, defoliants were sprayed on trees to reduce enemy cover, and slash and burn cultivation methods were used for rapid food production and logging for resources. These actions resulted in a rapid decline of forest habitat and have long-term effects on the regeneration of forests in this region. Where forest remains, it is often highly fragmented, which hinders the movements of lorises.

Pygmy slow lorises are hunted and their parts are dried and sold in markets as traditional medicines to cure ailments from headaches to broken bones, particularly in Cambodia. Additionally, following a series of online videos showing pygmy slow lorises being kept as pets, the number of people eager to keep them as pets has increased. Lorises kept as pets or as props for tourist photos are subjected to a great deal of suffering; their teeth are often pulled to prevent their venomous bites and they are often kept in cramped, brightly lit, and unsuitable conditions. Bright lights are damaging to their large nocturnal eyes and disruptive to their mental health. This trade often involves removing lorises from the wild, further damaging the already declining wild population.

One unforeseen problem the illegal trade has caused is the unintended translocation of wild pygmy slow lorises to regions away from their native home. Some rescue centers that receive captured pygmy slow lorises have released these primates to forests far away from where they were captured. Though these centers have good intentions when releasing captured lorises, it has made studying native wild populations, particularly from a taxonomy perspective, difficult. This is because researchers would have to question if the pygmy slow lorises they are studying were naturally found in that area or if they were artificially introduced.

Conservation Efforts

The pygmy slow loris (Nycticebus pygmaeus) is listed in Appendix I 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. The Appendix I listing means that commercial international trade is completely prohibited. The pygmy slow loris is protected under Vietnam law, which prohibits any exploitation of the species.

The NGO International Animal Rescue recently launched a campaign to educate people about the suffering caused to slow lorises by the pet trade in the hope of deterring them from participating in this trade.

However, further action is needed to protect the pygmy slow loris and prevent its population from decreasing in the wild. More research is needed to assess population size, distribution, and trends, and to accurately assess the threats to this species. Additionally, further conservation actions are needed to protect and manage the remaining forest inhabited by the pygmy slow loris.

References:

  • Cabana, F., & Plowman, A. (2014). Pygmy slow loris Nycticebus pygmaeus-natural diet replication in captivity. Endangered Species Research23(3), 197-204.
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  • Nekaris KA-I, Campbell N, Coggins TG, Rode EJ, Nijman V (2013) Tickled to Death: Analysing Public Perceptions of ‘Cute’ Videos of Threatened Species (Slow Lorises – Nycticebus spp.) on Web 2.0 Sites. PLoS ONE 8(7): e69215.
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  • Alltheworldsprimates.org
  • https://animals.sandiegozoo.org/animals/pygmy-slow-loris
  • https://lemur.duke.edu/discover/meet-the-lemurs/pygmy-slow-loris
  • http://www.nocturama.org/en/xanthonycticebus-a-new-lorisid-genus-for-the-pygmy-loris/

Written by Acima Cherian, July 2022