Pig-Tailed Langur, Simias concolor
PIG-TAILED LANGUR
Simias concolor
Geographic Distribution and Habitat
Pig-tailed langurs are endemic to the Mentawai archipelago islands of Indonesia and were listed as one of “The World’s 25 Most Endangered Primates” in the 2018-2020 publication coauthored by the International Union for Conservation of Nature, Global Wildlife Conservation, and other renowned conservation organizations.
They live in the forests along the hilly regions of these islands. They have also adapted to living in secondary forests (forests that have regrown after they have been cut down) and swamp forests, which have increased due to logging and agricultural activities.
They prefer lower levels of the canopy, where they can easily reach the ground to travel fast or run from predators if necessary.
They are also called simakobu monkeys or pig-tailed snub-nosed monkeys.
Pig-tailed langurs are colobines (leaf-eating monkeys). Yet, some of their features are not found in most other colobines, such as short tails, sexual swellings in females,equal-sized limbs better suited for terrestrial life, and a snub nose. This has led to some classification debates. Currently, they are considered a separate species under the genus Simias with two subspecies, Simias concolor concolor (found in the southern islands) and Simias concolor siberu (found in the northern island of Siberut). Pig-tailed langurs used to be named Nasalis concolor, “Nasalis” referring to a genus of odd-nosed monkeys, and researchers suggest reclassifying the pig-tailed langur as Nasalis due to their odd nose shape and genetic similarity to the proboscis monkey (Nasalis larvatus).
Size, Weight, and Lifespan
Males weigh between 16.9 -17.3 pounds (7.7- 7.9 kg), and females are smaller, weighing 11.5- 15.4 pounds (5.2-7.0 kg). Mean body length is about 20 inches (52 cm) in males and 18.1 inches (46 cm) in females. Their tails are short, about 6 inches (15 cm).
As of this writing, their average lifespan is unknown.
Appearance
At first glance, pig-tailed langurs look like sagely old men with a shock of the backward-combed hair on their crowns and large tufts of hair poking out near their ears (much like “Doc” from the “Back to the Future” movies). They have brown eyes that peer intensely into the forest. Their nose bridge is long and sweeps down to a small nose and flared, slightly upturned nostrils (therefore, they are sometimes called snub-nosed monkeys).
If you saw just their tail, you would not guess you were looking at a monkey. They are the only colobine with a short tail, and this unique feature inspired their common name. Their tails are mostly hairless and curly towards the end, much like a typical pig’s tail.
Pig-tailed langurs are dichromatic, meaning both males and females can be found in two color morphs or variations. Grayish-black fur is the most common color morph among adults. This variety usually has a lighter-colored crown and multicolored appearance near the neck (the strands of fur here are made of different colored bands in a pattern called “agouti”). The males with this color morph also have a tuft of white hair around their penis. A smaller population can be found with the second color morph, with cream-buff colored fur. White cheek patches and black on the face, hands, and feet are standard to both color morphs.
Males and females are visually distinct or sexually dimorphic, with males being about 25% heavier and 13% larger than females. Males have large canines (almost double the length of a female’s canines) that they use to intimidate other males.
Diet
Pig-tailed langurs are colobines, a group of Afro-Eurasian leaf-eating monkeys, who feed mainly on leaves. They can also eat fruits, seeds, and flowers.
Leaves, especially mature ones, contain a lot of fiber in the form of lignin and cellulose. Fiber is notoriously difficult to digest, and leaves take a lot of time to be broken down to release their sugars (which gives energy for the monkeys’ activities). To help with leaf digestion, pig-tailed langur stomachs have developed into a complex set of fermentation chambers that can store leaves for a while before going to the intestines. These fermentation chambers collect the leaves and soften them with digestive fluids. They also have specialized bacteria that help break down leaf fiber. This system also allows the monkey to gobble a lot of leaves because the leaves are held in these chambers before slowly being released to the rest of the digestive system.
Behavior and Lifestyle
They are active during the day (diurnal), and they seem to be comfortable in trees (arboreal) and on the ground (terrestrial). Anatomically, pig-tailed langurs’ arms and legs are about the same length, which suggests that they are better suited to walking on the ground (monkeys that swing from trees have longer arms or legs). But pig-tailed langurs seem equally comfortable moving through the tree canopy using all four limbs. They do not move through the trees as fast as truly arboreal primates.
When they sense danger, their first instinct is to freeze and hide in the dense canopy of the forest. If the threat approaches them, they drop to the ground and run. The sudden fall of 6 to 8 monkeys from trees creates crashing branches and loud noises, which hopefully startles the potential threat enough to give the monkeys time to get away.
Pig-tailed langurs are the only colobine (leaf-eating monkey) with a short tail, which looks more like the curly tail of a pig than a monkey’s tail.
They have two color morphs (dichromatic) with a grayish coat coloration and a pale-buff coloration.
They are conformable traveling through the canopy (arboreal) and on the ground (terrestrial).
They were designated as one of the world’s 25 most endangered primates in a 2018-2020 publication of the same name.
Pig-tailed langurs live in one-male groups (OMG) of 8 to 9 individuals consisting of multiple adult females and their offspring, including juveniles and sub-adult males.
When they wake up, usually at dawn when the temperature is cool, male pig-tailed langurs make loud calls to let other langurs know they survived the night and can still defend their territory. After this, one family member (male or female) leads the group to find food.
As folivores, they do not typically spend much time traveling or searching for food because leaves are abundant in the forest. However, they have to eat a lot of leaves to acquire enough energy for their daily activity. Also, leaves have a lot of fiber, which takes a long time to digest. Therefore, pig-tailed langurs spend almost the same amount of time resting as they do eating so that they can completely digest whatever foods they have eaten. Most of the resting time occurs during the afternoon during the hottest time of the day.
Before the sun sets, the family will gather in the dense foliage of a tree and settle down to sleep.
The pig-tailed langurs’ social structures are highly variable. They live in monandrous groups with one female or multiple females and all-male bachelor groups. The dynamics of the adult males and other females seem relatively peaceful. Most antagonistic behaviors are limited to males of different troops.
As social forest-dwelling dwellers, pig-tailed langurs use a lot of vocalizations to communicate because, in dense foliage, it is easier to hear than see each other. All colobines are famous for making loud calls, and only male pig-tailed langurs make loud nasal barks that can travel through the forest for 546 yards (500 m). He usually makes this call first thing in the morning, which triggers males from other troops to join to form a chorus. Large males have large lung capacities and can make louder calls. So, these loud calls advertise the strength and size of males to others to deter confrontation for food or females.
Both males and females have specific calls for potential threats. For example, their calls for elephants and pigs (not a threat to them) sound different from their alarm calls for humans (who hunt them and are their biggest threat). As expected, they are on high alert when they detect humans. They even have unique calls and related responses for different predators. For example, felid or cat predators have mostly been eradicated in the pig-tailed langur habitat. Hence, they are not an existing threat, unlike human hunters. When a group of pig-tailed langurs was played a recording of felid predator sounds and human hunter sounds, the monkeys made different calls and had a more urgent response to the human hunter sounds.
They have a polygynous mating system (one male mates with multiple females). Pig-tailed langur social systems are understudied, and this has caused some confusion among researchers. Previously, they were classified as monogamous groups because of limited observations of one male and one female group. Typical monogamous pairs comprise one male and one female that mate for a year or more, but pig-tailed langur males prefer to form family groups with multiple females. To avoid confusion with the monogamous social pairs, scientists often refer to polygynous primates that sometimes exist in one-male-one-female groups as monoandrous. Studies in undisturbed environments have shown that monoandrous groups are unstable and formed due to hunting of habitat change pressures that affect the primate’s social behavior.
Mating may be somewhat seasonal, and infants were observed to be born between November and July. Pig-tailed langur females have a reproductive region between their hind legs that swells when they are ready to mate. These swellings increase with the level of the estrogen hormone in the body, which increases the chance of the female successfully becoming pregnant. In social groups with more females than males, there is a lot of competition among females for male attention. In such cases, being able to advertise their reproductive potential through visually obvious swellings reduces the competition because only a few females will be ready to mate at a time.
Pig-tailed langurs usually give birth to one infant. Twins are rare. The mother is in charge of parental care, while the father protects the troop. We do not know if other females help take care of young that are not their own. Mothers practice “infant parking” where they leave their young alone in tree canopies for 2 to 3 hours while the mother forages for food.
Both males and females disperse from their natal troop (where they were born). Dispersal can happen as adults, but it is most common in juveniles and subadults who leave to form a family group. Dispersal helps prevent inbreeding between closely related individuals from the same troop. Sometimes, subadult males may form an all-male group of bachelors if they cannot find females to create a group with.
Pig-tailed langurs have overlapping habitats with other primates, such as the Mentawai langur (Presbytis potenziani). On an island with limited resources, you would think there is a lot of competition between two primate species living in the same area. However, these species share or partition their resources by eating different types of food. Pig-tailed langurs eat mainly leaves, while the Mentawai langurs tend to eat more fruits and seeds.
Many of their natural predators (wild cats and leopards) have been eradicated from the forests of Mentawai. Pythons and some eagle species may occasionally prey on pig-tailed langurs, but human hunters are their largest threats.
Foliovores play an essential role in maintaining plant diversity in forests. They eat leaves and create light gaps in densely packed canopies. Light gaps allow smaller plants on the forest floor to receive much-needed sunlight, giving them a chance to grow in an environment usually dominated by tall trees.
The International Union for Conservation of Nature lists pig-tailed langur as Critically Endangered (IUCN, 2015), appearing on the IUCN Red List of Threatened Species.
Habitat destruction and hunting are the biggest threats to pig-tailed langurs. Island ecology relies on a delicate balance of plant and animal life for a forest to be stable. Humans have deforested much of Indonesia’s natural resources to expand human development (homes, agricultural land, roads, etc.). Commercial logging for timber and palm oil plantations has caused Indonesia’s most significant scale of habitat destruction. Removing large numbers of trees can lead to soil erosion by rain and rivers, which prevents other plant species from establishing themselves there. The lack of trees leads to a shortage of shelter and food resources for wildlife. On an island, animals have few options for traveling far for these resources. Thus, endemic species like the pig-tailed langur that are only found on the Mentawai islands are more threatened by environmental changes compared to primates on the mainland.
The pig-tailed langur is a preferred protein choice among local hunters. These primates are even part of ceremonial hunts and local people’s cultural rituals. Hunters have upgraded their bows and arrows to rifles, making hunting expeditions more successful. Sometimes, pig-tailed langurs are kept as pets, especially if captured as young monkeys. However, these primates do not survive long in captivity.
Since 1994, their population has declined by an estimated 73-90%, and it continues to decline.
The pig-tailed langur 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.
Indonesia has laws that protect pig-tailed langurs. Their northern range is relatively protected from logging activities and deforestation, especially Siberut National Park. The pig-tailed langur population in this region is highest at about five individuals per acre (53 individuals per sq. km).
Local participation is the best conservation effort against unsustainable hunting. Some organizations work with local people and hunters to help protect the primates, who are a big part of the people’s culture and identity. Researchers benefit from local knowledge and the opportunity to study pig-tailed langurs. Locals benefit from ensuring that their natural resources persist and their traditional practices can be passed on to future generations.
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Written by Acima Cherian, November 2024