Miller’s Grizzled Langur, Presbytis canicrus
MILLER'S GRIZZLED LANGUR
Presbytis canicrus
Geographic Distribution and Habitat
The Miller’s grizzled langur (Presbytis canicrus), also known as Miller’s langur, Miller’s grizzled surili, Kutai gray langur, or even the “Dracula monkey”, is native to Indonesia. In fact, it is endemic to the island of Borneo, which means that it is found nowhere else in the world. Borneo is considered a biodiversity hotspot, as it is home to a huge array of endemic animal and plant species, with a particularly rich diversity of primates. Miller’s grizzled langurs make their homes in the lush rainforests of the island, living from the lowlands up into the hills. The main areas of the island in which they are known to live are the Sangkulirang Peninsula, the Wehea Forest, and Kutai National Park, although their population in the latter has been significantly reduced in the last fifty years. They can be found at elevations up to 5,250 feet (1600 m), though are usually found from sea level to 3,300 feet (1000 m). Miller’s grizzled langurs are exceptionally rare. Not only is their population very small and shrinking every day, they are also elusive and spend their time in the high canopy, making research into the species very difficult.
Formerly considered a subspecies of the Hose’s langur as P. hosei canicrus, the Miller’s grizzled langur was elevated to full species status after a taxonomic review in 2014.
Size, Weight, and Lifespan
Miller’s grizzled langurs range in size from 19 to 22 inches (48 to 56 cm) without their tail. Their tail adds another 26 to 33 inches (65-84 cm) in length. They weigh about 13 lbs (6 kg) on average, with males slightly on the heavier side. Langurs typically live to about 25 years of age.
Appearance
Miller’s grizzled langurs are medium-sized monkeys, with the exceptionally long arms, legs, and tail that one might expect from an acrobatic tree-dweller. They are gray over most of their bodies (“grizzled” means to be streaked with gray), with darker heads, hands, and feet. Their bellies are light gray or white. They have a “cape” of long white fur around their neck, explaining their alternate name of “Dracula monkey”. They can be distinguished from the closely related white-fronted langur (P. frontata) as they have a white spot underneath their nose, in contrast to the white spot on the forehead of white-fronted langurs.
Diet
Like other colobines, those species in the subfamily Colobinae, Miller’s grizzled langurs are considered folivorous, or leaf eaters. Their diet is centered around leaves and shoots, which make up about two-thirds of what they eat. However, the rest of their diet is very diverse, including seeds, flowers, eggs, small prey like bird nestlings, and even mud, which provides them with important minerals.
Mother Nature fitted these leaf-eating monkeys with large, multichambered sacculated stomachs—similar to those of cows. This specialized stomach, with the help of essential, symbiotic gut bacteria (microflora), efficiently breaks down cellulose fibers in the surilis’ leaf-laden diet. Large salivary glands and elongated intestines lend their own assistance in the overall digestive process.
Their ingestion of mud can result in the formation of bezoar stones in their stomachs. Bezoars are hard clumps of undigested material that can get stuck in the gastrointestinal tract. While they can cause medical issues, they are typically harmless. Consuming salt and minerals from a mud puddle on the ground is one of the few reasons that a Miller’s grizzled langur ever leaves the safety of the canopy.
Behavior and Lifestyle
Miller’s grizzled langurs are diurnal, meaning they are awake during the day, and arboreal, meaning they live nearly their entire lives in the trees. They spend most of their time in the upper canopies, about a third of their time in the lower canopies, below 65 feet (20 m), and almost never come to the ground. They move about by leaping and via brachiation—swinging on branches from their arms.
Miller’s grizzled langurs are so rare that, not long ago, they were feared extinct. Extinction concerns were first raised in 2004 and continued until 2011 when a team of scientists spotted the incredibly rare monkey unexpectedly in the Wehea Forest, where it was not known to live at the time. The langurs were even featured on the Animal Planet television show “Extinct or Alive” in 2019. While they were not actually believed to be extinct by the time the episode aired, the show’s footage of a grizzled langur was the first video evidence of the species in the 21st century and one of the first conclusive sightings of the monkey since 2011. Both of these sightings happened when a langur was caught licking salt and minerals from a puddle on the ground—a testament to how elusive they are in the canopy.
Miller’s grizzled langurs were featured as the titular role in Leo Berenstain’s 1994 book “The Wind Monkey and Other Stories”, a collection of stories based on Indonesia’s traditional culture and its clash with Western society.
A typical group of Miller’s grizzled langurs consists of one adult male, two to four adult females, and their offspring, with an average group size of eight individuals. As incredibly rare primates, very little is known about their day-to-day lives. Other langur species are known to be fairly territorial, defending their home ranges from other groups. Single males may loosely band together in bachelor groups. Females are often the ones that lead the group’s movements, while males take charge of defending the group. As suitable habitats are destroyed, langur populations are often forced into increasingly small areas, which increases intergroup conflict.
The communication tactics of Miller’s grizzled langurs are not well studied. However, based on other Presbytis species, they likely use a large variety of vocalizations. For example, males may use calls to indicate their presence to other groups, and hopefully ward them off. Alarm calls are likely used, which warn groupmates of nearby predators. Miller’s grizzled langurs likely also use a variety of body postures and facial expressions to communicate with others.
Very little is known about the reproductive lives of Miller’s grizzled langurs. Other colobines are polygynous, meaning that each male mates with multiple females. Based on their group structure, this is likely true of Miller’s grizzled langur as well. They likely have a gestation period of about 200 days or around six and a half months. It is unknown what role the father plays in rearing young. In some other related species, other female group members help to raise the baby, even if it’s not theirs, a behavior known as “alloparenting”.
Miller’s grizzled langurs are sympatric with—that is, they live in the same locations as—white-fronted langurs (P. frontata) and maroon langurs (P. rubicunda). They are likely preyed upon by snakes and birds of prey.
The International Union for Conservation of Nature lists the Miller’s grizzled langur as Endangered (IUCN, 2015) appearing on the IUCN’s Red List of Threatened Species. This assessment is based on ongoing dramatic population loss, which is approximately proportional to the rate of habitat loss that the monkeys have experienced. Where habitat still exists, hunting pressure is strong. Over the last 20 years, the Miller’s grizzled langur population has dropped by about 50%, and this loss is expected to continue without immediate conservation action.
A major cause of habitat loss is the destruction of forests to establish oil palm plantations. Palm oil is a common ingredient in many snack foods today, but, while it is economically cheap to produce, it places an exceptional burden on the native people and animals that are displaced to make it. Oil palms need warm tropical climates to grow—the same climates that have become biodiversity hotspots over millions of years. Approximately 90% of the world’s palm oil comes from just a handful of islands in Indonesia and Malaysia. When forests are cleared for palm oil plantations, suitable habitats become patchy. Arboreal animals like Miller’s grizzled langur are forced to travel between forest patches on the ground, leaving them vulnerable to predator attacks and hunting.
Forest fires have also caused historic population loss among Miller’s grizzled langurs. In the 1980s and 90s, extensive forest fires and droughts attributed to the El Niño climate pattern caused habitat destruction and a subsequent dramatic drop in population in Kutai National Park, one of only two areas in which it was known to exist at the time. About 95% of the original forest of the park was destroyed by 1998. The population in the park was severely reduced and has never recovered. While this drop in population was attributed to a natural disaster, humans have reduced the monkeys’ resiliency—their ability to bounce back after a catastrophe. By causing rampant habitat loss and fragmentation, the langurs cannot easily travel between patches of remaining habitat. More monkeys can’t easily enter Kutai National Park due to the loss of suitable habitat outside of it, so the langurs left within suffer from reduced genetic diversity. Additionally, because of human-caused climate change, storms, droughts, forest fires, and other natural disasters will become increasingly frequent and intense, leading to more stress on an already fragile population.
Miller’s grizzled langurs are also commonly hunted. They are prized for their bezoar stones, which are thought by some to bring good luck or to have healing properties. They are hunted for these stones despite the fact that only a small number of the langurs ever have one. Because there is no way for the hunters to target monkeys with bezoar stones, many monkeys end up needlessly being killed to find each stone.
Miller’s grizzled langurs are 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. They are also protected at the federal level under Indonesian law, though enforcement of this law is weak. More research is needed into the geographic boundaries of the species so that better habitat protection can be achieved.
The Dayak tribe, a community of indigenous people that live in Borneo, has made significant strides in protecting Miller’s grizzled langurs. The Wehea forest of eastern Borneo, which, in 2011, was discovered to host a population of the langurs, is protected by the Dayak tribe. Rangers from the tribe patrol the forest and protect it from illegal logging, fires, harvesting, and plantations. The Wehea forest, together with the surrounding forests, make an oasis for Miller’s grizzled langurs in a landscape that is otherwise subject to rampant habitat destruction.
Ehlers Smith, D.A. 2014. The effects of land-use policies on the conservation of Borneo’s endemic Presbytis monkeys. Biodivers Conserv 23, 891–908. https://doi.org/10.1007/s10531-014-0639-0
Lhota, S., Loken, B., Spehar, S., Fell, E., Pospech, A., Kasyanto, N. 2012. Discovery of Miller’s Grizzled Langur (Presbytis hosei canicrus) in Wehea Forest confirms the continued existence and extends known geographical range of an endangered primate. Am J Primatol.74(3):193-8. doi: 10.1002/ajp.21983. PMID: 24006537.
Nijman, V. 2010. Ecology and Conservation of the Hose’s Langur Group (Colobinae: Presbytis hosei, P. canicrus, P. sabana): A Review. In: Gursky, S., Supriatna, J. (eds) Indonesian Primates. Developments in Primatology: Progress and Prospects. Springer, New York, NY. https://doi.org/10.1007/978-1-4419-1560-3_16
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Written by K. Clare Quinlan, May 2024