ROBINSON’S BANDED LANGUR
Geographic Distribution and Habitat
Robinson’s banded langurs naturally occur in the northern peninsula of Malaysia, South Myanmar, and Thailand. They live in tropical and subtropical forests but have adapted to secondary growth and agricultural plantations. Though there are no published estimates of their population, Robinson’s banded langurs are widespread and have a larger range than many other langur species that live in the same geographical region.
The Robinson’s banded langur was once considered a subspecies of the Raffles’ banded langur, Presbytis femoralis, that are found in nearby Singapore. However, despite their similar appearance, genetic research has shown that Robinson’s banded langurs are a separate species and not any more closely related to the Raffles’ banded langur than any other langur species.
Size, Weight, and Lifespan
These medium-sized slender monkeys usually weigh 11–12 pounds (5–8 kg), with males being slightly heavier. Otherwise, males and females look similar. Other than their size difference, they are sexually monomorphic. Their bodies measure between 17–21 inches (43–55 cm) and their much longer tails are between 24–33 inches long (62–83 cm).
We do not know many specifics about the ecology and lifestyle of Robinson’s banded langur. We assume that these aspects are similar to closely related langurs that live nearby, like the Raffles’ banded langur. We think that the Robinson’s banded langur has a lifespan between 15–18 years in the wild.
These monkeys have a characteristic pointed cap of fur on their head and large dark eyes that peer through a relatively small head. They are covered in dark black-brown fur all over their body except for white stripes under their limbs. These white stripes are clearly visible when the langurs sit in trees with their legs splayed for balance.
Robinson’s banded langurs have bare skin on their lips and bright white eye rings, which distinguish them from the otherwise similar-looking Raffles’ banded langurs.
Many banded langur species bear newborns with white or light-gray fur, which is in stark contrast to the dark fur of the adults. The young one’s light fur blends with the white stripes along the inner limbs of the adults. Females carry their young across their bellies and the white and dark contrasting colors provide surprisingly good camouflage. If predators were to look up at the canopy from the ground, the white color of the baby against the dark fur of the mother blends with the bright sky above the canopy. And when aerial predators look down from the sky the mother’s fur looks like the dark forest floor.
Banded langurs are herbivores that eat young shoots and fruits but their diet mainly consists of leaves, which take a long time to digest. Leaves also have lower nutritional value than fruits, so leaf monkeys, like the Robinson’s banded langur, have to eat a lot of leaves to get enough energy to survive. To cope with this diet requirement, Robinson’s banded langurs have multi-chambered stomachs that can hold a large amount of leaves and digest them in stages, which makes the nutrition extraction process more efficient.
Behavior and Lifestyle
Robinson’s banded langurs are diurnal and mostly arboreal (tree-dwelling). They are extremely good at navigating the forest canopy. They are sure-footed as they leap from branch to branch. Sometimes, especially before jumping or when young play, they stand on two legs. On the rare occasions when these monkeys descend to the ground, they walk quadrupedally, on all fours.
They use their long tails to balance while they sit on branches and reach out to grab leaves or fruits. They are highly alert animals and if you do see them in the wild, they are usually high in the canopy looking around for knowledge.
Robinson’s banded langurs have prominent white eye-rings and bare lips, which sets them apart from Raffles’ banded langurs.
They make loud cackling calls before dawn.
Research on Robinson’s banded langur is very limited. There are no estimates of how many exist in the wild.
There are many uncertainties about Robinson’s banded langur ecology and behavior but, in general, tropical banded langurs tend to follow these daily patterns. Eating and digesting leaves takes up most of the day in a banded langur’s life. Langurs usually wake up just before dawn and the family or troop prepare to go foraging for leaves and fruits. In the cool mornings, they travel across the forest canopy, picking green leaves and eating as much as possible. As the day warms up, these monkeys rest, which allows time for their stomachs to digest leaves. Younger langurs may spend this time playing and others may groom each other (allogrooming). Before sunset, the family settles in at their sleeping sites high up in the canopies for the night.
Vocal communication is important among banded langurs especially because it is difficult to pick up on visual signals when dense vegetation blocks their view of each other. Robinson’s banded langurs are known for the cackling calls they make just before dawn. These dawn calls probably communicate the fact that langurs made it through another night and that they will be on the move to forage for food soon.
Robinson’s banded langurs tend to be shy and difficult to observe directly. Additionally, because of the previous taxonomic confusion in species, most studies are limited to other banded langur species and not specifically the Robinson’s banded langur. These reasons have resulted in a gap in our knowledge of how these monkeys interact and communicate with each other. We assume that family and troop interactions are peaceful like other similar-sized banded langur troops.
Langurs live in social groups (with 3–20 individuals) led by a dominant male and multiple females and young langurs. Females have a gestation period of about 6 months and give birth to one offspring at a time. Baby banded langurs are born with light-colored fur, which becomes darker when they become more independent from their mothers. Young banded langurs are carried everywhere by their mothers for at least the first year of their lives. They get their complete black-brown fur before they become full-fledged adults. Juvenile banded langurs are usually considered adults when they reach about 5 years old. At this stage, males usually leave their natal troop and join other males to form a bachelor group. Females stay with their natal troop and only leave if they join another male to form a family group of their own.
Folivores or leaf-eating monkeys play an important role in cycling nutrients between trees and the soil. The monkeys digest large amounts of leaves and deposit scat on the forest floor, which is broken down into valuable nutrients for plant growth.
In sunny tropical climates, trees do everything they can to produce more leaves and soak up more sun so that they can maximize photosynthesis, the food-making process in plants. However, this means that larger trees provide too much shade and other, smaller trees and plant species do not get enough sunlight to grow. Banded langurs, such as the Robinson’s banded langur, eat lots of leaves and limit the growth of these large trees, which opens up pockets of sunlight for other plants.
As prey to large birds and reptiles, banded langurs are an important food source for predators and part of a complex ecological network that maintains the balance of the ecosystem.
The International Union for Conservation of Nature lists Robinson’s banded langur as Near Threatened (IUCN, 2020), appearing on the IUCN Red List of Threatened Species.
The habitats of Robinson’s banded langurs have been steadily decreasing due to agriculture and human development. Banded langurs have been moving into rubber and oil palm plantations to find enough food and space. Therefore, there is an increase in human-primate conflicts, and farmers will kill the monkeys that eat or destroy crops.
Robinson’s banded langurs are sometimes kept as pets and are tragic victims of animal trafficking. Most primates that are illegally traded die during the capturing and transport process in the pet trade industry.
The Robinson’s 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.
There have been no surveys or estimates to determine how many Robinson’s banded langurs are left in the wild. Organizations like the IUCN and WWF have programs in Myanmar and Thailand that work with communities and habitats to provide safe areas for primates, including the Robinson’s banded langur. National parks in Malaysia, Thailand, and Myanmar offer safe refuges for native wildlife. However, the environmental damage due to human expansion and habitat loss is severe enough that scientists expect the population of Robinson’s banded langurs to continue decreasing.
- Ang, Andie, Dewi Imelda Roesma, Vincent Nijman, Rudolf Meier, Amrita Srivathsan, and Rizaldi. “Faecal DNA to the rescue: Shotgun sequencing of non-invasive samples reveals two subspecies of Southeast Asian primates to be Critically Endangered species.” Scientific Reports 10, no. 1 (2020): 9396.
- Ang A & Jabbar S (2022) Raffles’ Banded Langur: The Elusive Monkey of Singapore and Malaysia. World Scientific, Singapore, 100 pp.
- Ang, A., Boonratana, R. & Nijman, V. 2021. Presbytis robinsoni. The IUCN Red List of Threatened Species 2021: e.T39806A205875703. https://dx.doi.org/10.2305/IUCN.UK.2021-3.RLTS.T39806A205875703.en. Accessed on 09 September 2023.
- Freund, D., M. Signs, and K. Yoganand. “Primates of the Greater Mekong: Status, Threats and Conservation Efforts. WWF-Greater Mekong. 74p. Published in 2021 by WWF-Greater Mekong (World Wide Fund For Nature). Any reproduction in whole or part must mention the title and credit the publisher as mentioned above as the copyright owner.” (2021).
- Md-Zain, BADRUL MUNIR, MUHAMMAD NURISMADEE Abdul-Manan, M. A. B. Abdul-Latiff, N. O. R. L. I. N. D. A. Mohd-Daut, and A. R. Mohd-Ridwan. “Positional behavior of Robinson’s banded langur (Presbytis femoralis robinsoni).” Journal of Sustainability Science and Management 14, no. 5 (2019): 164-174.
- Miller, G.S., 1934. The Langurs of the Presbytis Femoralis Group. Journal of Mammalogy 15, 124.. https://doi.org/10.2307/1373983
Written by Acima Cherian, August 2023