BORNEAN SLOW LORIS

Nycticebus borneanus

Geographic Distribution and Habitat
The Bornean slow loris (Nycticebus borneanus) lives in the central and southern portions of Borneo in the Indonesian provinces of West, South, and Central Kalimantan.

All Bornean varieties of slow loris were previously thought to be the same species. Known scientifically as Nycticebus menagensis, and commonly as the Bornean slow loris, three subspecies had been identified: Philippine slow loris (N. m. menagensis), the Bornean slow loris (N. m. borneanus), and the Bangka slow loris (N. m. bancanus). In 2013, compelling research into their face masks established that these subspecies were likely more different than previously assumed and the argument followed that they—as well as another new variety known as the Kayan River slow loris (Nycticebus kayan)—should each be considered a distinct species.

The effects of this transition are still felt in conservation and research today. As nocturnal animals, difficult to study extensively in the wild, the histories of several slow loris species are quite chaotic. Research is only just beginning to reveal the full extent of slow lorises’ biological diversity. Where once there were only two species considered wholly distinct, there are now eight, with more possibly waiting in the wings.

This longstanding taxonomic confusion makes it difficult to know the full geographic distribution of many slow loris species, including the Bornean slow loris. The areas in which the creatures live may be more numerous than currently thought. Additionally, we may never know if a species might have once been found somewhere where, in the meantime, it has gone extinct. Inversely, due to being heavily trafficked, species of slow loris may now exist in an areas where they are not actually native.

Bornean slow loris geographic range. Map: IUCN, 2020

Size, Weight, and Lifespan
A Bornean slow loris is about 10 inches (26 cm) in length. The average weight of this species is not recorded and its lifespan is currently unknown.

Appearance
Species of slow loris share the same basic appearance. Though their sizes do vary, all are quite small. They have furry bodies, round heads, short ears, and broad flat faces. The big toes on their hind feet are opposable, giving them the exceptional gripping power essential to moving through the trees. Their most prominent features are their large, forward-facing eyes. These capture every scrap of light available to them during their late-night forages.

Bornean species, like the Bornean slow loris, are only subtly distinct from others. Though only apparent under close examination, one distinguishing feature is their lack of a second upper incisor. Bornean species also have signature face masks, a discovery that, in 2013, split the conglomeration of subspecies formerly comprising Nycticebus menagensis into four distinct species, with one of these being the Bornean slow loris.

A Bornean slow loris is distinguished by a dark face mask. The rings around his eyes never extend below his cheek bones. He sports another dark spot of fur on top of his head and a lighter stripe runs between his eyes.

Photo credit: 7layersoflands/Creative Commons

Diet
Slow lorises are omnivorous. They primarily forage for a variety of leaves, fruits, seeds, berries, gums, saps, and bird eggs but also hunt arthropods and sometimes even small vertebrates like lizards.

Due to living in biodiverse habitats, a slow loris’s dietary needs are particular to the ecosystems where it lives.

Saps are an especially crucial part of a slow loris’s diet. Deprived of these and her other natural staples, a slow loris in captivity quickly grows malnourished and dies.

The diet of the Bornean slow loris has not been properly assessed.

What Does It Mean?

Arboreal:
Physically adapted to living primarily or exclusively in trees.

​​​Arthropod:
An invertebrate animal (one with no spine) having an external skeleton, a segmented body, and jointed appendages. Includes insects, spiders, crustaceans, and myriapods.

Biodiversity: 
​The level of variation of life in an ecosystem, biome or the entire planet. Biodiversity is a measure of the health and function of an ecosystem.

Haplorhini:
Sometimes spelled Haplorrhini. “Dry-nosed” primates (from the Greek for “simple-nosed”), a suborder of primates containing the tarsiers. Old World monkeys, apes, and New World monkeys.

Incisors:
Narrow-edged teeth at the front of the mouth, adapted for cutting.

Nocturnal: 
Active at night.

Omnivorous:
Having a diet that consists of food of both plant and animal origin.

Polyandry:
A pattern of mating in which a female animal has more than one male mate.

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.

Strepsirrhine or strepsirhine: 
Relating to the primate suborder Strepsirrhini, consisting of lemurs, lorises, and bush babies, who characteristically have moist areas around their nostrils.

Taxonomy: 
A branch of science that encompasses the description, identification, nomenclature, and classification of organisms.​

Visit the Glossary for more definitions

Behavior and Lifestyle
A slow loris is arboreal with limbs uniquely adapted for this lifestyle. Her hands and feet all have opposable digits that enable her to keep a firm grip at all times. Her style of locomotion closely resembles crawling; bringing one hand forward, her opposing foot follows. Her pace is slow and her movements methodical. While other arboreal primates typically swing and leap to cover gaps in the foliage, her own method is far less dramatic—though still exceptionally acrobatic! With only her feet latched to their perch, she reaches toward the next with her entire body, holding herself aloft with incredible balance and poise. When her two hands are wrapped firmly around the target branch, she hoists herself onto it, continuing on her way without skipping a beat.

With no way to actively protect herself against attacking predators, her best defense is in keeping as low a profile as possible so as to avoid them altogether. Moving silently and scrupulously is just one of the many cryptic strategies she uses to this end. In fact, this need to remain under the radar and out of harm’s way is so key to her survival that it distinctly shapes her way of life. She also eludes predators by foraging under the cover of darkness. Her two large and sensitive eyes give her exceptional night vision. With these, she can attend to her forage while keeping her sharp sense of smell and keen hearing attuned to her surroundings, wary of any misgivings. Of course, her cryptic maneuvers advantage her as a hunter as well. A cicada who unfortunately crosses her path will likely never realize until he’s already in the process of being gobbled up.

Some researchers have theorized that a slow loris’s markings have evolved to mimic the form of a cobra. Though in no way a perfect imitation, it is perhaps just close enough to make a predator wary of getting close enough to find out for certain, lest it is a deadly cobra in the end.

Oddly enough, like cobras, a slow loris is venomous. Specialized glands hidden in her underarms secrete a special oil. When this oil mixes with her saliva, a toxin is created. She may spread the toxin through her fur with her tongue. This not only renders her an unsavory snack for larger predators but also helps to manage and kill pesky infectious parasites. If actively under attack, she uses her extremely powerful bite to inject the venom into her attacker. When given, a slow loris bite is powerful enough to send a grown human into anaphylactic shock!

Her specialized glands are also used in her ritual of scent marking. As strepsirrhine primates, slow lorises have wet noses. This feature makes them highly receptive to smell—a sense that has diminished in many of the other primate lineages. As she crawls through the rainforest, she dutifully transfers her oils to the various substrates she passes. She also leaves her trace by urinating wherever she goes, a behavior researchers call “rhythmic urination.” Her scent marks are not used to mark her territory but as a way of communicating with other slow lorises.

Like so many primates, she is a social creature. Once more, however, her need to keep a low profile greatly influences the means by which she socializes with others. Congregating in large groups would make her and her fellow slow lorises far too visible, making them vulnerable to predators. Instead, scent marking is a way of communicating and bonding with members of her spatial group. By leaving her scent in various ways as she traverses her range, she keeps members of her spatial group privy to her movements. In the same manner, she remains knowledgeable of theirs. Scent marks also allow her to attract potential mates and even help them to track her down in the dense jungle. Once one has located her, the more physical means of their courting can commence.

The inner workings of slow loris social behavior are complex and not yet profoundly understood. Each species likely has its own unique set of mannerisms, rituals, and social dynamics that help individuals to recognize each other and bond as groups. For now, the socially driven behaviors of the Bornean slow loris remain uninvestigated.

Daily Life and Group Dynamics 
A Bornean slow loris wakes at night. Having spent the daylight hours asleep, he emerges from his hiding spot resolved to forage.

He sets off, moving delicately but persistently through the trees. He hardly makes a noise. His large eyes search the branches for a meal. Spotting a tasty leaf, he uses his two grasping feet to anchor himself to his perch before reaching out with both hands to grab it and bring it to his mouth.

Solitary and self-reliant, he spends most of his night hunting and foraging alone. His inclination toward solitude by no means makes him an unsocial creature, however. His range overlaps with several other members of his particular species. These individuals comprise what researchers call his “spatial group.” Like him, the other members of his group lead mostly solitary lives. However, as they make their nightly forages, each of them leaves behind scent marks. When other members happen upon one of these scent marks, they learn a great deal of information about the group member who left it.

Generally, no more than two members of the same spatial group encounter each other at one time. When this happens, they may or may not completely ignore each other. If they choose to connect, they are likely to spend time grooming one another.

Again, the social workings of slow lorises are not well understood at this time and those of the Bornean slow loris need further investigation.

Daily Life and Group Dynamics 
A Bornean slow loris wakes at night. Having spent the daylight hours asleep, he emerges from his hiding spot resolved to forage.

He sets off, moving delicately but persistently through the trees. He hardly makes a noise. His large eyes search the branches for a meal. Spotting a tasty leaf, he uses his two grasping feet to anchor himself to his perch before reaching out with both hands to grab it and bring it to his mouth.

Solitary and self-reliant, he spends most of his night hunting and foraging alone. His inclination toward solitude by no means makes him an unsocial creature, however. His range overlaps with several other members of his particular species. These individuals comprise what researchers call his “spatial group.” Like him, the other members of his group lead mostly solitary lives. However, as they make their nightly forages, each of them leaves behind scent marks. When other members happen upon one of these scent marks, they learn a great deal of information about the group member who left it.

Generally, no more than two members of the same spatial group encounter each other at one time. When this happens, they may or may not completely ignore each other. If they choose to connect, they are likely to spend time grooming one another.

Again, the social workings of slow lorises are not well understood at this time and those of the Bornean slow loris need further investigation.

Fun Facts

The distinct face mask of the Bornean slow loris is the feature responsible for its 2013 recognition as its own species.

The Borenean slow loris has a venomous bite, strong enough to send a grown human into anaphylactic shock.

Communication
Slow lorises make fantastic use of their olfactory sense for communication. As strepsirrhine primates, they have wet noses that give them better smelling capabilities than their haplorrhine cousins (who have evolved to have dry and, therefore, less sensitive) noses. By relying on scent to communicate, slow lorises are able to maintain their low profiles while still keeping in touch with members of their spatial groups.

As she moves about, a slow loris leaves scent marks in her wake. She may rub the toxic oils from her brachial glands onto various substrates or use her urine. Some evidence suggests scent marking is particularly important to mating rituals. However, this behavior has only been studied in a select few species. While Philippine slow lorises undoubtedly communicate using scent, it is possible that they use scent marking for communcation unique to their species. We will not know until the issue has been properly researched.

Slow lorises do not make alarm calls, as this would make futile their cryptic strategies for defense. However, for all their efforts to remain undetected, slow lorises do use vocalizations to communicate. Of the species of slow loris that have been studied so far, their repetoires consist of a variety of calls. Whistles and short keckers are probably used to show affiliation while snarls, grunts, screams, and long keckers are almost definitely signs of aggression. The Bornean slow loris likely makes some, if not all of these sounds—and may even make others of which we are not yet aware!

Research shows that Javan slow lorises make ultrasonic vocalizations that are beyond the range of human hearing. This gives them the ability to communicate at a frequency unheard by predators who might be nearby. However, this subject remains to be investigated in other slow loris species.

The ways in which slow lorises communicate are probably unique to their species—perhaps even their own spatial groups! Therefore, those in which Bornean slow lorises communicate, while not altogether inconceivable, will remain ultimately unknown until research sheds light on them.

Reproduction and Family
Little is currently known about the mating rituals and familial relationships of Bornean slow lorises. The nocturnal life styles of slow lorises make thorough study of them difficult for human researchers. Furthermore, what little has been observed in one species cannot necessarily be assumed to be the case for others. As a result, the minuter details of their habits remain difficult for us to apprehend.

Generally speaking, a female attracts a male using scent marks that signal to him her readiness to mate. Following her marks through the jungle, the male eventually locates her. In some species, a female initiates copulation by whistling while she hangs upside-down from a branch by her feet.

There is some debate as to whether or not slow lorises are monogamous or polyandrous. It likely varies depending on the species. Whatever the case, the mother seems to take complete responsibility for raising her offspring. The birth of more than one slow loris at a time is rare event.

She leaves her newborn hidden in a nest while she leaves to forage. In case any predators should find him, she applies a coat of her toxic oils to his fur. Eventually, he develops the muscles and skills to leave the nest to join his mother on her nightly forages. It is likely from her that he learns the survival and social skills the development of which will transform him from a helpless youth to the self-reliant creature a slow loris ultimately becomes.

Captured Borean slow loris Photo credit: Wibowo Djatmiko/Creative Commons

Ecological Role
The ecological role of the Bornean slow loris is not understood at this time.

Conservation Status and Threats
The Bornean slow loris listed as Vulnerable by the International Union for Conservation of Nature (IUCN, 2015) appearing on the IUCN’s Red List of Threatened Species, and announced this assessment in the summer of 2020. Tere has been a more than 30% reduction in population over three generations (approximately 21-24 years) as a result of collection for the pet trade and extensive habitat loss. Although the species is adaptable to anthropogenic change, forest loss has been so severe that it is likely to have had some negative impacts, with Borneo losing a third of its forest in less than 25 years, also due to extensive fires. Bornean slow loris populations are decreasing.

The species was assessed to some extent with the IUCN’s 2008 evaluation of Philippine Slow loris (nycticebus menagensis), of which it was considered a subspecies at that time. This taxonomic saga sheds light on the risks of unintentionally misrepresenting species based on insufficient data. When species are more biologically diverse than science previously assumed, it takes years for conservation efforts to catch up. In that time, the situations in which those previously unrecognized species find themselves are likely to grow more precarious.

Indeed, misunderstanding the taxonomy of slow loris species has proven problematic for their conservation both generally and locally. While researchers wrestle with the raw data, conservationists may occasionally misidentify the individual slow lorises that wind up in their care. Since taxonomy determines what they should be fed, how they should be socialized, and where they should be released if they are eventually rehabilitated, proper care and rehabilitation is dependent on proper species identification.

This issue of taxonomy is doubly important given the sheer number of slow lorises that end up in rescue and rehabilitation centers. The biggest threat to all slow loris species is their value as commodities in the exotic pet trade and for traditional medicines. Slow lorises are illegally trafficked and sold all over the world. Buyers rarely have any concern about what variety of slow loris they are receiving. When rescued from these circumstances, a slow loris is inevitably already in rough shape. Suffering from infection, malnutrition, and blindness and highly stressed by his ordeal, there is no room for error in getting him what he needs as fast as possible. Therefore, proper rapid identification is essential to his rescuers’ success.

Unfortunately, poached from the wild, a slow loris’s chances of survival are small—and rehabilitation leading to her release even smaller. Even if she is brought back to optimal health, a single consequence of her ordeal remains that will permanently prevent her eventual release. When she was first taken, her captors prepared her for sale. By removing her teeth—an incredibly painful procedure typically done without any kind of anesthetic—they prevent her from biting their future owners and injecting them with her venom, which can prove fatal. However, with this one action, she, a competent and self-reliant creature, is rendered helpless and dependent for the rest of her life. For without her teeth, she cannot eat and she cannot defend herself. Ultimately, she has no hope of ever rejoining the wild.

While life in the wild is certainly preferable to life in captivity, slow lorises who avoid becoming pets are still threatened by human encroachment into their natural habitats. When left to their own devices, slow lorises often prove to be quite adaptable and capable of surviving in suboptimal conditions. In many places where they live, however, forests have been degraded to the point where it significantly and adversely effects their rates of survival—and fragmentation of their ranges inevitably inhibits healthy gene flow between spatial groups. What’s more, such trends put them at even greater risk of being found, captured, and sold into the pet trade.

Some populations of Bornean slow lorises likely live in one of the last and largest stretches of continuous ancient forest left in Southeast Asia. Known as the Heart of Borneo, this vast stretch of forest is less than half of what the island once supported. In the last thirty years alone, illegal logging, the construction of dams and other infrastructure, mining, slash-and-burn agriculture, and many other human activities have drastically depleted Borneo’s wilderness, putting the animals that call it home—including many humans themselves—at great risk.

The Heart of Borneo, for now, remains intact. But these trends have not let up. Compounded with the overarching effects of climate change, the future for the Bornean slow loris’s home appears bleak. Slash-and-burn agriculture has become especially problematic over the years. With its peat forests and swamps, Borneo is highly vulnerable to fire. When a fire ignites in one of these environments it can smolder invisibly underground for weeks. In the wake of such fires, the scorched soil more easily erodes, preventing the forests from ever recovering. September 2019 saw some of the worst fires on record, many of which had been set intentionally in order to clear the land for palm oil plantations. So long as the Heart of Borneo is at risk, so too is the Borenan slow loris.

Conservation Efforts
The Bornean slow loris is still awaiting proper evaluation by the IUCN. More research regarding the species’ taxonomy, distribution, and behaviors would paint a clearer picture for how to best conserve this unique species of primate.

Direct efforts to conserve the Bornean slow loris are scarce. Fortunately, a number of conservation efforts do serve to benefit the lives of Bornean slow lorises, if only indirectly. For instance, the species likely resides within a number of protected areas across Borneo.

The Bornean slow loris must also benefit from the Heart of Borneo Initiative. This is a trilateral agreement between the three countries of Borneo (Indonesia, Brunei, and Malaysia) to work in cooperation to sustainably manage the last remaining rainforests of Borneo, using the largest of them—the one known as the Heart of Borneo—as their focal point. Their efforts to protect, research, and educate others about the biodiversity of these ancients rainforests is paramount to the survival of the Bornean slow loris—not to mention all of the creatures who call these rainforests home.

References:

  • http://www.sci-news.com/biology/article00775/
  • https://www.researchgate.net/publication/233958577_Taxonomy_of_the_Bornean_Slow_Loris_With_New_Species_Nycticebus_kayan_Primates_Lorisidae
  • https://jvat.biomedcentral.com/articles/10.1186/1678-9199-20-43
  • https://www.biorxiv.org/content/biorxiv/early/2017/04/19/078535.full.pdf
  • https://wwf.panda.org/knowledge_hub/where_we_work/borneo_forests/borneo_deforestation/
  • http://www.heartofborneo.org/about-us/
  • https://news.mongabay.com/2007/05/experts-borneo-in-urgent-need-of-protection/
  • https://www.iucnredlist.org/species/39760/10263652
  • https://www.nationalgeographic.org/photo/bog-borneo/
  • https://www.nytimes.com/2019/09/17/world/asia/indonesia-fires-photos/
  • https://www.wwf.or.id/en/about_wwf/whatwedo/forest_species/where_we_work/kayan_mentarang/
  • https://www.wwf.or.id/en/about_wwf/whatwedo/forest_species/where_we_work/kayan_mentarang/collaborative_management.cfm
  • http://pin.primate.wisc.edu/factsheets/entry/slow_loris/behav
  • https://www.int-res.com/articles/esr2015/28/n028p087.pdf
  • https://jvat.biomedcentral.com/articles/10.1186/1678-9199-19-21

Written by Zachary Lussier, May 2020. Conservation status updated July 2020.