Raffles’ Banded Langur, Presbytis femoralis
RAFFLES’ BANDED LANGUR
Presbytis femoralis
Geographic Distribution and Habitat
The Raffles’ banded langur is native to the southern tip of Malaysia and the island nation of Singapore. Their distribution and habitat are limited to small pockets of forests. In Singapore, they are mostly found in the Bukit Timah and Central Catchment Nature Reserves. While in Malaysia, they are only found in the states of Johor and Pahang. These regions are characterized by humid tropical jungles with lots of plant and animal diversity.
Raffles’ banded langurs used to be widespread in the early 20th century but most of the native forests were cut down for agriculture and human development. Today small populations of Raffles’ banded langurs can be found in secondary-growth and swamp forests.
These langurs get their name from the British colonial officer, Thomas Stamford Bingley Raffles, who is considered the founder of modern Malaysia and Singapore. When he was gifted a young primate, Sir Raffles recognized his pet as a new species, and the first Raffles’ banded langur was described by zoologists in 1838. Until then the Raffles’ banded langurs lived most of their lives in taxonomic obscurity and were grouped as a subspecies with other banded langurs. Banded langurs around Malaysia and Sumatra look similar to each other and separating them into species based on their appearance alone is difficult. It took genetic-level tests to figure out that the langurs in Southern Malaysia were the same species as the Raffles’ banded langurs identified in Singapore. The Raffles’ banded langur taxonomy was finally elevated to a separate species in 1986.
Size, Weight, and Lifespan
Raffles’ banded langurs are the largest non-human primates in Singapore. Adults can weigh 13-18 pounds (6-8kg) and grow between 1-2 feet tall (60-65 cm), not including their tail length. Their tails are longer than their bodies and can measure up to 2.6 feet (80 cm). This means that the tail alone is as tall as an average 2-year-old human! You would think that lugging this long tail would be bothersome, but Raffles’ banded langurs use their tails to help them balance on branches as they quickly move through the forest. If you have ever tried to walk on the sidewalk curb, you will know that it is easier to balance on the narrow ledge with your arms outstretched. With their long tails, banded langurs can use their arms to hold food and grab onto branches while their tails help them keep balance on narrow tree limbs.
Raffles’ banded langurs have not been successfully reared in captivity and so we do not know what their lifespan could be, but from our knowledge of other langurs, researchers think that Raffles’ banded langurs probably live for 15-18 years in the wild.
Appearance
Raffles banded langurs have the typical langur appearance—a small face and a pointy cap of fur. They have dark rusty brown-black fur all over their body except for their belly and inner thighs that have wispy grayish-white fur. They have distinct white eye-rings and deep brown eyes. Males and females look similar so they are not sexually dimorphic.
Unlike the dark fur of the adult, baby Raffles’ banded langurs are born with striking white fur over most of their body and cross-shaped black stripes along their back. We may think newborns stick out with this bright white fur, but the pattern breaks up the shape of the baby when they are carried across their mother’s belly. The white fur blurs against the adult gray belly fur and the black stripes merge with the rest of the adult fur. When the young become more independent around 8-10 months, their white fur eventually sheds and new dark fur grows to resemble the adult’s dark coloration
These langurs may appear gangly with their long arms, legs, and tail but these features are perfectly suited for their lives in the trees.
Each langur has distinct facial features that may not be immediately obvious to most people, but researchers have used high-resolution photographs to carefully differentiate between individual monkeys. The population of Raffles’ banded langurs is small enough that researchers are able to identify individual monkeys and follow their lives for multiple years.
Diet
Raffles’ banded langurs are herbivores that feed on some flowers and fruits, but they mainly eat leaves—which is why they are sometimes called banded leaf monkeys. Raffles’ banded langurs can even feed on non-native and toxic plants, like rubber trees (Hevea brasilinensis), that other primate species avoid. However, they are also picky about what they eat. From one tree they may eat only the flowers and not the leaves, and then from another tree, they choose only the seeds and not the flowers.
Leaves are a good source of fiber and minerals, but it takes extra effort to digest leaves to give the langurs energy for their activities. So raffles’ banded langurs have to eat a lot of leaves and spend most of their day foraging for food.
To tear through tough leaves, Raffles’ banded langurs have sharp molar teeth. To digest these strong plant materials, they have a large, specialized multi-chambered stomach. In these different stomach compartments, the langurs can store food in digestive juices and allow gut bacteria to help break down the tough fiber and sometimes toxic materials.
Behavior and Lifestyle
Raffles’ banded langurs are diurnal (active during the day) and arboreal (tree-dwelling). They rarely descend to the ground and prefer traveling through the high canopy, often leaping several feet across from one tree to another. They use their long limbs to elegantly navigate the forest canopy with their tail held out for balance. When they feed or rest they usually sit on tree limbs.
Like most leaf monkeys, Raffles’ banded langurs forage for most of the day and spend hot afternoons resting and digesting their food. The dominant adults will often lead the way to suitable foraging trees and wait for members to catch up.
These banded langur species are generally shy and difficult to observe in the wild. Researchers have spent many hours in humid forests patiently waiting, looking for, and observing Raffles’ banded langurs. Once the monkeys get used to humans, the langurs (especially the juveniles) express curiosity and approach the researchers to get a closer look.
Families are close-knit and most interactions seem supportive and peaceful. When they are not feeding or traveling they spend time grooming each other or the young play and explore. Fights between families are usually observed when bachelors try to separate females from the natal troop (the troop they were born in) to form their own family group. These aggressive interactions can lead to injuries.
Recently, researchers observed Raffles’ banded langurs grooming long-tailed macaques (Macaca fascicularis), a much smaller primate species, which is rare in the wild. Grooming usually happens between family members. Often lower-ranking adults groom the more dominant individuals. Grooming in primates can be viewed as a social transaction—a literal case of “you scratch my back and I’ll scratch yours.” The one being groomed gets their fur cleaned of parasites and the groomer gets a snack of insects or crumbs from a previous meal. Apart from the hygiene benefits of grooming, the social interaction also reaffirms bonds (like the positive feelings you may get while hugging family or friends). The close interaction between two different primate species may indicate that they do not compete for the same resources. Similar inter-species grooming has been noted in captivity where individuals are limited to a confined space. It is possible that forest fragmentation has created similar confined situations and the two species are more likely to interact in these habitat patches. Either way, these observations tell us that there is a lot more we need to learn about how these primates interact with their community of forest dwellers.
- Raffles’ banded langurs are the largest non-human primate in Singapore.
- They have large multi-chambered stomachs that can digest leaves and toxins.
- Baby Raffles’ banded langurs are born with white fur and cross-shaped black strips of fur on their back.
- They communicate in high-frequency calls that travel short distances.
- Raffles’ banded langurs have been observed grooming long-tailed macaques.
Raffles banded langurs form two types of social groups. One is a typical family led by a dominant male who safeguards multiple females and their young that he has fathered. The other is a bachelor group that consists of multiple males that have left their natal troop.
A family can have as many as 13 members with one male leader who mates with 3–4 adult females, each of whom can have one infant and a few juveniles. Family members are affectionate and their interactions are often lively with disobedient young ones and yelling adults, so much so that researchers have grown to appreciate their personalities. Though babies are mostly cared for by their mothers, once the young become more mobile, other females or aunts will help carry and care for the young. The dominant male is not only protective of his family but is also playful and affectionate with his young.
Bachelor groups have between 4 and 5 adult or subadult males. Members will help look out for predators and warn the entire group if a threat is near so males can safely forage for food even without being part of a typical family. Males in a bachelor group will search for females that they can take from a troop and form a family with.
Vocal communication is important in tropical forests, where group members cannot see each other. Dominant Raffles’ banded langur males will warn their family of danger by making a rapid-fire “ka-ka-ka” alarm call.
They often use high-frequency sounds (they sound like high-pitched voices to us) to communicate, unlike other leaf monkeys. These sounds can only travel short distances and researchers think that this communication method evolved because Raffles’ banded langurs have always lived in smaller forests, and in close-knit families. Being able to communicate effectively across short distances means that messages will get sent directly to family members without being intercepted by other langurs and energy is not wasted in trying to unnecessarily send messages far away.
Pregnancy in female Raffles’ banded langurs lasts about 6 months. Mothers usually give birth to one infant at a time and the timing of the birth is not predictable in many cases but it is usually dependent on how healthy she is and how much food is available. So in Singapore, female Raffles’ banded langurs tend to give birth either during the summer monsoons (May–July) or the winter monsoons (November–January). This phenomenon is not seen with the langurs in Malaysia and it is an example of the complex relationship between animal biology and the environment.
Baby langurs are vulnerable to the many dangers of the forest, such as predators and falling from trees. So for the first year or so of their lives, they are carried everywhere by their mother, who keeps a tight leash on her child’s movements and activities. With the baby clinging to her belly, the mother will navigate through the forest canopy to find food and even take dizzying leaps across canopies!
At around a year and a half, young Raffles’ banded langurs are called juvenile. Juveniles can be identified by their behaviors, they are extremely curious and quite brave, often approaching researchers to get a closer look.
These langurs reach puberty between 4 and 5 years of age, at which stage they are called subadults. Male subadult langurs start getting antsy and ready to leave their natal troop. These males may join other males to form a bachelor group or they may search for other females so that they can form their own families. Females tend to stay part of their natal group unless they leave or are taken to form a family.
Raffles’ banded langurs are considered adults at about 5 years old, when they reach their full size.
Raffles’ banded langurs are part of a complex forest ecosystem where all the wildlife and plant species work in a balanced flow of energy and matter. Despite their small numbers, Raffles’ banded langurs play specific roles that maintain the tropical forests in Singapore and Malaysia and allow the habitat to sustain itself.
As fruit eaters, Raffles’ banded langurs disperse seeds through the forest. Seeds are either thrown away as the fruits are eaten, or they are packed in fertilizing langur feces and deposited away from the parent plant, which means that the seed can successfully grow into a tree with less competition for space and sunlight.
Raffles’ banded langurs are also seed eaters or predators, which means that they help control or minimize the over-population of certain tree species. They have a similar role as folivores or leaf-eaters. Sunlight is a valuable resource for trees whose growth is limited by the amount of light it gets to make food or photosynthesize. By eating a large number of leaves, langurs help control the spread of any one tree canopy, allowing multiple trees and species to cohabit in the ecosystem.
Raptors like the changeable hawk-eagle (Nisaetus cirrhatus) are the main predators of Raffles’ banded langurs, making them part of the forest food web.
Raffles’ banded langurs are one of the many primate and mammal species that live in the tropical jungles of Singapore and Malaysia. They are able to share their niche with other primates by feeding on plants other species cannot eat. This ecological plasticity or flexibility to adapt to a new food source is one amazing trait of the Raffles’ banded langurs. In this way, they have taken up a new niche and continue performing the ecological roles of seed disperser and plant population control, which is vital to the overall functioning of their ecosystem.
The International Union for Conservation of Nature lists Raffles’ banded langurs as Critically Endangered (IUCN, 2022), appearing on the IUCN Red List of Threatened Species. This means that the species are rare and in severe threat of extinction if conservation actions are not taken. Their low population numbers and decreasing habitat has reduced genetic diversity among Raffles’ banded langurs, which affects their ability to successfully reproduce and grow.
As of 2021, there are about 300 Raffles’ banded langurs in Malaysia, and 68 individuals in Singapore. Habitat loss is the main cause for the declining Raffles’ banded langur population. Singapore and Malaysia have a long colonial history of converting native forests into palm and rubber tree plantations for economic purposes. The development of roads has further divided forests into smaller patches, which forces langurs to travel on the ground to move between habitats, which in turn results in unfortunate vehicle accidents. Human encroachment into the langurs’ habitat has also introduced predators like domestic dogs that are known to kill Raffles’ banded langurs.
In Malaysia and, particularly, Singapore, there are only pockets of forested areas that can adequately provide enough space and food to support langur families. And these habitats are shared with other primates and competitors. Multiple families of Raffles’ banded langurs need to thrive for a population to be stable. Given that females give birth to only one young at a time and there are at least 2 years between births, the rate of their population growth is slow. This means that even small reductions to their habitat can have devastating effects on the survival of these langurs.
The Raffles’ banded langur 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. This Appendix rating is usually given to species where trade and trafficking are not a major concern. The rarity and elusiveness of Raffles’ banded langurs make trapping and transporting these species logistically difficult.
Between 1935 and 1951, Singapore made major political changes to preserve their existing natural resources, including setting aside national parks where development was prohibited. Given Singapore’s small size, any nationwide effort to maintain natural habitat is beneficial to wildlife species, especially more adaptable primates like the Raffles’ banded langur.
The Raffles’ banded langurs were close to extinction and, to halt their decline, the International Union on the Conservation of Nature formed the Raffles’ banded langur working group that is dedicated to research and conservation of the species. They form agreements between governments using science-based approaches that will support the reproduction and survival of wild Raffles’ banded langurs in their natural habitat.
To solve the habitat connectivity issue and reduce langur road kills, conservation professionals have made rope bridges that connect forest canopies across roads and developments. These habitat corridor structures allow langurs to move from one forest patch to another searching for food or mates without going to ground.
Researchers and conservation professionals have successfully launched a program that uses citizen science or contributions by the public as a way to gather data about Raffles’ banded langurs. This not only increases their ability to observe the langurs but also generates awareness of their conservation needs.
Raffles’ banded langurs have lived in small populations for many years and, as a relatively skittish monkey, they were poorly studied for most of the 20th century, especially compared to other primates. Many considered their population to be too small to survive in their rapidly changing environment. However, the Raffles’ banded langurs are resilient. Despite small populations and inbreeding, with some level of habitat protection from the governments, they were able to adapt to feeding on non-native plants, navigating past roads, and ultimately surviving and successfully reproducing. Currently, the langurs are protected within national parks, but still vulnerable outside of the parks, particularly to road accidents.
- Ang, A., D’Rozario, V., Jayasri, S.L., Lees, C.M., Li, T.J., Luz, S. 2016. Species Action Plan for the Conservation of Raffles’ Banded Langur (Presbytis femoralis femoralis) in Malaysia and Singapore. IUCN SSC Conservation Breeding Specialist Group, Apple Valley, MN, USA.
- Ang, Andie, and Sabrina Jabbar. (2021). Raffles’ Banded Langur: The Elusive Monkey of Singapore and Malaysia. World Scientific.
- Ang, Andie, Sabrina Jabbar, Vilma D’Rozario, and Jayasri Lakshminarayanan. “Citizen science program for critically endangered primates: A case study from Singapore.” Primate Conservation 35 (2021): 179-188.
- The Integrated Taxonomic Information System (ITIS). Presbytis femoralis (Martin, 1838). https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=573042#null. Retrieved February, 2023.
- Jonathan Ho Kit Ian (30 Aug 2020). Presbytis femoralis – Banded Leaf Monkey. https://wiki.nus.edu.sg/display/TAX/Presbytis+femoralis+-+Banded+Leaf+Monkey. Last modified on 30 Aug 2020. Retrieved February, 2023
- Lee, Zan Hui, Andie Ang, and Nadine Ruppert. “First record of interspecies grooming between Raffles’ Banded Langur and Long-tailed Macaque.” Journal of Threatened Taxa 13, no. 9 (2021): 19246-19253.
- Ow, Sebastian, Sharon Chan, Yuet Hsin Toh, Su Hooi Chan, Jayasri Lakshminarayanan, Sabrina Jabbar, Andie Ang, and Adrian Loo. “Bridging the gap: assessing the effectiveness of rope bridges for wildlife in Singapore.” Folia Primatologica 1, no. aop (2022): 1-12.
Written by Acima Cherian, February 2023