Geographic Distribution and Habitat
The Javan surili (Presbytis comata), also known as the grizzled leaf monkey, Javan leaf monkey, or Javan grizzled langur, is native to the volcanic island of Java, one of four tropical islands that comprise Indonesia’s Greater Sunda Islands (the three others being Borneo, Sulawesi, and Sumatra). Found mostly in West Java, this leaf-eating colobine monkey also occupies fragmented pockets of Central Java, congregated around Mt. Sawal, Mt. Dieng, Mt. Lawu, and Mt. Slamet. Of all Indonesia, Mt. Slamet receives one of the highest annual rainfall amounts, averaging 179 inches (450 cm) with a reported maximum of 264 inches (671 cm).
Tall, primary forests are the species’ preferred habitat. But the conversion of these rainforests into human settlements, agricultural farmland, and plantations—which has occurred over centuries—has isolated Javan surili populations from one another. Historically, these monkeys have resided at elevations of up to 8,530 feet (2,600 m). But as their forestlands continue to dwindle, the surilis are, with increasing frequency, forced to dwell within disjointed fragments of their former range. They survive on forested volcanic slopes too steep to cultivate; in remnant primary forests; and in secondary, lowland, and upper montane forests. They are found at the edges and interior of this diminished habitat, showing a preference for the middle and upper layers of the forest canopy. Occasionally, they can be found on plantations (which had once been forestland).
Javan surilis are Colobinae, or leaf-eating monkeys, a subfamily of the Old World primate family. Other members include 61 species in 11 genera; among them are black-and-white colobus monkeys, large-nosed proboscis monkeys, and gray langurs. Individuals are formally referred to as colobines and casually referred to as leaf-eaters.
In recent years, the genus Presbytis has undergone significant taxonomic changes that include shuffling and reshuffling species and subspecies. To point, a scientific debate persists as to whether the Javan surili is the “parent” species to two “children”; namely, the subspecies:
- Javan grizzled langur (comata comata) of West Java
- Javan fuscous langur (comata fredericae) of Central Java
Genetically, both these purported subspecies are distinct from one another. But a chain of “intermediate populations” between the two (an outcome of interbreeding, resulting in no morphological differences in offspring) has cast doubt.
Some scientists have asserted that the Javan fuscous langur is most certainly a distinct species, while other scientists have said, “No, the Javan fuscous langur is neither a distinct species, nor a subspecies, but rather it is one and the same as the Javan surili,” or “conspecific.” To support their opposing theories, differing scientific camps cite morphological gradations in the primates’ coat coloring. Whether these nuances in coat color are insignificant or definitive is unresolved. Embedded in this scientific kerfuffle is the taxonomic status of the Javan grizzled langur—which remains uncertain.
Sidebar taxonomic family drama: Before receiving their own respective genus, lutungs (Trachypithecus) and gray langurs, aka Hanuman langurs (Semnopithecus), were classified as subgenera of surilis (Presbytis).
Size, Weight, and Lifespan
Sexual dimorphism—that is, the distinct differences in size or appearance between the sexes of an animal—apart from their reproductive organs, is unremarkable in the species. Fully grown adults weigh between 13 and 18 pounds (6–8 kg), with an average weight of 14 pounds (6.4 kg). Individuals can grow as tall as 3.5 feet (108 cm).
Nature has fitted surilis with long, thin tails that range from about 20–33 inches (50–85 cm). Their nonprehensile tails, a characteristic of Old World monkeys, are used for balancing, rather than for grasping.
Lifespan is unknown for most surili species in the wild. Captive Sumatran surilis are reported to live 18 years or more, but whether the lifespan of these island neighbor surili cousins can be applied to Javan surilis is speculative.
Okay, so first of all: how can anyone not love this expressive little face? Chestnut-colored eyes peer out from beneath a wild, furry cap that encroaches upon an unassuming brow ridge. The dark facial skin is bare of fur, and the slender nose is dotted with demure, downward-pointing nostrils that breathe in the scents of the rainforest. An untamed, long mane frames the surili’s face and hides its small ears.
Javan surilis’ coat color varies from a whitish tone in some populations to dark gray or almost black in others. Bright white fur on the chest, abdomen, inner limbs, and underside of their long tail gives contrast to those with dark coats. Javan surilis get their “grizzled” appearance (and nickname) from the mix of hair colors interspersed within their thick coats. These Old World monkeys are further characterized by a slim build (apart from their little pot belly), long torso, relatively long legs, and thin arms.
Predominantly a folivorous species (meaning that they eat mostly leaves), Javan surilis also eat fruits, flowers, seeds, and the occasional large tree snail, plus they might nibble on the tips of branches. They favor young leaves over mature leaves, and their preferred leaves are from ficus plants (Ficus pubinervis), grenadia (Passiflora lingularis), millaa millaa vine (Elaeagnus trifloral), and a shrub known in the Javanese language as ki puyu (Schefflera aromatica).
Preferred fruits are from aromatic flowering plants in the Lamiaceae family (Premnda parasitica), flowering plants of the Actinidiacea family (Saurauia), and sarangan (Castanopsis argentea). Surilis intuitively know to avoid sweet succulent fruits such as figs (a favorite of orangutans and chimpanzees)—which can acidify their body’s neutral pH level (the measure of acidic/basic water balance) and disrupt digestion.
While Mother Nature neglected to give surilis cheek pouches as she did for their Old World primate cousins of the Cercopithecine subfamily (who include baboons and macaques), she instead fitted these leaf-eating primates 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.
Behavior and Lifestyle
The behavior and lifestyle of these primates are not well documented. Here’s what we know:
Javan surilis are both arboreal, spending most of their time in trees, and diurnal, active during daylight hours.
About 23 percent of their day is spent foraging and feeding; 21 percent is spent traveling; 5 percent is spent on other activities, such as socializing and grooming; and a whopping 51 percent of their day is spent resting! (Activity budget is based on Javan surilis living in Gede-Pangrango National Park, West Java, as observed/recorded by researchers.)
In between rest periods, these monkeys engage in three to four feeding bouts. They travel and feed in the upper canopy, leaping from tree to tree to advance. Overnight, they sleep in the tallest trees along volcanic ridges.
Humans are the predators that Javan surilis need to fear. Should they feel threatened, Javan surilis flee through the middle layers of the forest.
Studies focused on the Javan surili’s neighbor, the spangled ebony langur (Trachypithecus auratus), also known as the East Javan langur, have led wildlife biologists to conclude that Asian colobine monkeys are unable to taste natural sugars and generally have a poor sense of taste. Receptors on the tongues of these primates do not function the same as with predominantly fruit-eating monkeys, who are sensitive to sweet tastes. This revelation makes all the more impressive the Javan surili’s ability to intuitively avoid fruits (such as figs) that might contribute to rapid overfermentation and lead to an increase in acid levels in the animal’s body.
Javan surilis live in small family groups, usually comprised of one adult male, several adult females, and their young. Occasionally, a second adult male is part of a group, but only one of the males is dominant. Surveys of populations residing at Mount Slamet, Central Java, record group sizes as ranging from 2 to 14 individuals (where a group of two is an adult mating pair). Central Javan populations are known to form mixed-species groups with neighboring spangled ebony langurs (Trachypithecus auratus).
Young males leave their natal group before reaching puberty. For a time, they may remain solo, or they may form temporary “bachelor” groups with other males before finding a new group where they might have luck instilling themselves as a dominant male. Outside males may join the group they vacated.
Adult females, especially those from larger groups, may leave home to join a smaller, neighboring group that resides at a higher elevation in a richer environmental habitat.
These are territorial monkeys and encounters with outside surili groups—whose home ranges sometimes overlap—are often hostile. Home range size observed in the geothermal field of Kamojang, West Java, is between 88 and 100 acres (35 to 40 hectares). Home range size observed in the region of Patengang, on West Java’s southern coast, is only 35 acres (14 hectares). Home range size has not been reported for the Central Java surili population.
As one of Indonesia’s Greater Sundra Islands, considered a world biodiversity hotspot, the island of Java is home to a panoply of wildlife species—many of which are found nowhere else in the world, and many who are at risk of extinction. These animals include the Javan gibbon, Javan rhinoceros, and Javan leopard—all Critically Endangered. Other threatened or endangered species include the Javan warty pig and the slow loris. Flying overhead is the endangered Javan hawk eagle.
Javan surilis use vocalizations and body postures to get their message across. Like many monkeys, adult males emit a loud call—also referred to as the long-distance call because of its ability to reverberate far away. This piercing call is applied to various situations, including: defending a troop’s resources, attracting a possible mate, locating fellow troop members while out foraging, and marking and defending territories.
Researchers have found that the typical Javan surili loud call is characterized by a staccato-like sequence with alternating exhales and inhales. As these calls are emitted, they increase in loudness and intensity. What’s more, researchers have confirmed from acoustic analysis of 100 surili male loud calls that these calls are distinct among surili/langur species. Researchers further believe that these distinct call structures can help to clarify taxonomic and phylogenetic (evolutionary) relationships between the species within the genus Presbytis.
Other than an adult male’s loud call, other troop members are fairly quiet. Of course, the vocal repertoire of Javan surilis may include other calls. But researchers have focused on the loud call in their studies; thus, documentation for other vocalizations is not available—contributing to the Javan surili’s enigmatic nature.
Posturing, as an intimidation tactic, may accompany an adult male’s loud call if he is defending his group’s territory.
Grooming has been reported in the species, but it appears to be an activity mostly performed by females. One report states that female Javan surilis might spend up to 5 hours a day grooming themselves—that’s a lot of self-care!
Sexual maturity occurs between the ages of 4 and 5. The mating system for Javan surilis is described as monandrous, similar to a monogamous mating system. In a monogamous relationship, a male and a female are exclusive lifetime breeding partners. However, in a monandrous relationship, a female will mate with one exclusive partner over a period of time, but the male gets to mate with several females during this period. Sounds like polygyny, when one male mates with multiple females. Confusing, yeah. The “timestamp” on a female’s devotion to one exclusive male breeding partner appears to distinguish monandry. A female’s inclination to disperse from her birth group, cutting ties with her male breeding partner, to seek out a higher-altitude environment with richer food resources—and a new male—is a survival tactic. Indeed, scientists believe that monandry is an evolutionary strategy, driven by environmental factors such as altitude, climate, and forest characteristics. While a group’s composition favors a monandrous system, further field research is necessary to determine the nuances of Javan surilis’ mating relationships.
Javan surilis have no so-called breeding season. After a gestation period of 5 to 6 months, a female gives birth to a single infant. Unlike other species of the genus Presbytis, the fur coat coloring of Javan surili newborns is medium to dark gray or black. A mother nurses her baby for one year. Moving through the forest, she carries her child ventrally (the infant clings to her stomach). During this period, she receives lots of help from other females in the group, who take turns caring for the infant (a practice known as “allomothering”). At one year old, an infant is considered weaned and becomes independent.
Their folivorous diet makes Javan surilis excellent pruners of their forested habitat. By picking the leaves of overgrown shrubs and trees, they help to rejuvenate new plant growth. Their consumption of fruits further helps to regenerate their environment. Seeds of the fruits they consume pass through their digestive tract and are excreted in their feces to become rich fertilizer.
The Javan surili is classified as Endangered by the International Union for Conservation of Nature (IUCN, 2015), appearing on the IUCN Red List of Threatened Species. Total population is uncertain, but the number of Javan surilis is decreasing along with their continually diminishing habitat.
Both subspecies, the Javan grizzled langur of West Java and the Javan fuscous langur of Central Java, are also classified as Endangered.
Population surveys from 1994–96 place the total population of Javan surilis at less than 2,500 individuals in 30 isolated locations. This number includes 1,400 to 1,500 mature individuals, with no more than 250 mature individuals in any subpopulation. Surveys conducted around Mt. Slamet in Central Java between 2006 and 2008 found between 1,172 and 1,621 individuals along the volcano’s southern and eastern slopes. When included with other population surveys, the total population size, according to the IUCN, is estimated to be less than 6,000. However, the Mount Slamet study focused on Javan fuscous langurs, which may or may not be a subspecies of the Javan langur; therefore, this total estimated population number may be skewed.
An article published in the Jurnal Primatologi Indonesia, Vol. 16, No. 1, January 2019, gives a more dire total population count of less than 1,000 Javan surilis remaining in our world.
Anthropogenic (human-caused) activities are the reason for this primate species’ grim situation. Forests are illegally logged—trees are felled for building materials, cut to obtain wild orchids and pitcher plants, or chopped down to be used as firewood. What remains are degraded, inferior forest fragments. As little as 4% of Javan surilis’ original and once-pristine habitat remains today.
Excessive hunting poses a secondary threat to the species, particularly around Mt. Slamet in Central Java. Here, the surilis are regarded as pests and crop raiders. Because of their occasional forays into agricultural areas to find food, the monkeys are shot and killed. Locals also kill the monkeys to eat their flesh, known as “bushmeat.”
Javan surilis are also victims of the illegal wildlife trade, particularly those dwelling in Central Java. According to the Indonesian conservation foundation ProFauna, Javan surilis are one of the most frequently traded primates, frequently sold online for about 500,000 to 1 million Indonesian Rupiah—which is a paltry $32.18 to $64.36 U.S. dollars.
Then there’s the world’s climate crisis, which threatens all wildlife species.
The Javan surili 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.
Javan surilis are known to occur in the following protected areas, all in West Java: Gede-Pangrango National Park, Mt. Halimun National Park, and Mt. Tukung Gede Nature Reserve.
Each of the two subspecies (if, in fact, these monkeys are true subspecies) occurs in a protected area. The Javan grizzled langur is found in Ujung Kulon National Park, West Java; and the Javan fuscous langur is found in Gunung Slamet Nature Reserve, Central Java.
To combat further forest destruction, conservationists advocate for currently nonprotected rainforests to receive a protection designation, either as a wildlife reserve, nature reserve, or national park.
If Javan surilis are to be saved from extinction, a balance must be achieved between the species’ preservation and the economic needs of the timber industries and the livelihoods of local citizens. In formulating successful conservation strategies, the diversity of food tree species and the level of forest disturbance due to logging activities are key considerations.
One approach, say conservationists, is to plant trees that are food resources to the surilis, trees intended for timber, and “multipurpose” trees, including those that provide nontimber forest products, such as cloves, coconut, mango, mangosteen, melinjo, rambutan, nutmeg, and guava. To monitor the success of this initiative, conservationists suggest that these trees can first be planted on government-owned plantations. Ultimately, the hope is that the enrichment of forests currently low in food tree species can expand the habitat of Javan surilis and provide suitable habitat for other endangered wildlife species.
Founded in 1994 in the city of Malang, East Java, under the local name Konservasi Satwa Bagi Kehidupan (Wildlife Conservation for Life), ProFauna foundation has since developed throughout Indonesia and remains actively engaged in the protection of forests and wildlife. A major tenet of ProFauna is that all wildlife species have intrinsic value to nature, and every species of wildlife should be allowed to live freely in nature—and humans are responsible for making this happen. In 2018, ProFauna activists staged a public campaign event in Magelang, Central Java, with the goal of getting local citizens to become more aware of and involved in Javan langur protection.
Written by Kathleen Downey, November 2022