A black crest poked through the sea of green. I focused my binoculars on this puzzling feature. For a while there was little movement. I waited silently though the sun was relentless and shade a luxury. I was surveying for mammals in non-protected areas in Tripura in Northeast India. The predominantly open landscape was a mosaic of plantations, jhum fields, and secondary bamboo dominated forests. Several minutes later, a dark arm emerged, casting aside a large leaf. The crest and what it sat on came into view. It was a female Phayre’s leaf monkey or Phayre’s langur (Trachypithecus phayrei).
With a furry triangular head, dark face, a whitish pink pallid patch around the mouth, long whiskers and a beard she looked wonderfully weird.
The monkey’s most striking feature, – the wide white rings around its dark eyes, is the reason why locals call it “chashma bandar”. Their spectacled looks have caused much confusion. The Phayre’s langur is often wrongly identified as the spectacled langur (Trachypithecus obscurus); a closely related species, very similar in behaviour and appearance and found in the Malay Peninsula.
Sizing them up
Males and females are only mildly sexually dimorphic (or differ a little) in body size. While females weigh between 6-7 kilos, males weigh around 8 kilos. These spindle-shaped, mid-sized langurs have lean, lanky bodies and big bellies. They are predominantly arboreal and spend a lot of time at heights between 5 and 50 metres.
Like many other langur species, the Phayre’s langur has a very long tail, longer than the length of its body. This tail is not prehensile, i.e., it is not used to hold or manipulate objects. Instead, the tail helps the primate maintain balance while traipsing on all fours along branches that differ in size and orientation. The long tail also helps them jump between trees, at times crossing wide canopy gaps.
Living on leaves
Phayre’s langurs are reported from a variety of habitats — ranging from primary to secondary, from evergreen and semi-evergreen to broadleaf, and from mixed and moist deciduous to bamboo dominated forests. They are also seen in plantations that are mixed or are monocultures, like tea estates. Is this variety of habitats possible because of a flexible diet?
Phayre’s langurs are colobines, the subfamily of old-world primates known for their specialised dietary adaptations to eating leaves. High in fibre, the diet of Phayre’s langurs is dominated by leaves and supplemented to varying degrees by fruits, seeds, flowers, shoots and the occasional invertebrate. One may think the ability to survive on leaves allows them to adapt to any habitat or cope better with habitat degradation and conversion. But thorough investigations have revealed that just any leaf won’t do.
Although leaves are abundantly available in their environment, Phayre’s langurs are very choosy. They eat a higher proportion of young leaves that they selectively harvest from certain plants. Immature fruits are eaten when young leaves are not abundant. These langurs do however eat a higher proportion of mature leaves compared to other Asian colobines. This suggests a stronger adaptation to a leafy diet.
Specialised teeth and stomachs help Phayre’s langurs digest and absorb nutrients from challenging food like leaves — high in plant fibre, and often laced in high concentrations of toxic and digestion inhibiting secondary compounds. Their molars have high ridges and cusps that enable them to break down cellulose, a substance in the cell wall that helps leaves stay stiff and strong. Being foregut fermenters, these monkeys have a complex, many chambered stomach — the reason behind their beautiful big bellies. To aid digestion, unique gut flora (symbiotic bacteria) breaks down food through microbial fermentation over long periods of rest. Therefore, if you ever come across a lounging, burping spectacle, legs adangle from a branch, rest assured that their gut flora is hard at work.
Gender dynamics and newborns
Phayre’s langurs live in groups that may have one to several males. Groups with many males are fluid — they regularly change back and forth between one- and multi-male groups. Occasionally, this results in the formation of new groups. Group sizes vary from half a dozen to over 30 monkeys. The males of the species stay and breed in their natal groups or leave to form new groups. The females regularly leave or are evicted from their natal groups to join other groups.
Within these groups, dominant males mate with several females. Females give birth to their first infant when they are slightly over five years old, following a gestation period of nearly 200 days. Babies are weaned off between 19 and 21 months.
The striking eye and mouth patches are seen in young and old individuals of either sex. All individuals except newborns have the mohawk like longitudinal crest. Newborns also differ in their coat colour. While the pink faced babies don bright orange coats, everyone else, including babies over eight months, have glossy greyish brown-black coats with whitish-yellow undersides.
The flamboyant natal coats are said to have evolved to attract non-maternal caretakers or alloparents. Like in other closely related species, baby care here is a communal affair. Unfortunately, these adorable brightly coloured babies with expressive faces have also drawn the attention of pet seekers and thus wildlife traffickers.
Threats to the Phayre’s langur
The Phayre’s langur was once widely distributed across eastern Bangladesh, Myanmar, southwestern China, Northeast India (Tripura, Mizoram and Assam), north of the peninsular zone in Thailand, Laos, and northern Vietnam.
Unfortunately, due to habitat loss, hunting and use in traditional medicine, and the illegal pet trade, the overall population had declined by greater than 50 per cent over a period of 36 years, as per an assessment in 2008. As the population was at a risk of becoming extinct, it was then listed as an endangered species in the IUCN Red List. However, there has not been an assessment of its conservation status in over a decade.
All habitat countries are also signatories to CITES (the Convention on International Trade of Wild Flora and Fauna), an agreement between governments that ensures international trade of wild animals does not threaten their survival. CITES lists Phayre’s langurs in Appendix II — that means, its trade is regulated and monitored. However, given that the species has almost been wiped out in large parts of its eastern range due to hunting and illegal capture, it is surprising that Phayre’s langurs have not been moved to Appendix I, where international trade is banned.
In India, the species is protected by the Wildlife Protection Act and has been awarded the highest level of protection listed as a Schedule-I species. Despite this they are severely threatened by habitat loss from large to small scale conversion of forests to tea, rubber, and timber plantations. Add to this, is habitat degradation brought on by expansion of human settlements, firewood collection, and charcoal production.
Despite the international conventions and national laws in place, ground realities portray a dismal future for this species. Perhaps, there hasn’t been more targeted action because these monkeys are considered locally common. This may be true in some areas, but what is also true is that the Phyare’s langur now exists in small isolated populations driven by habitat fragmentation. For a species with a fluid social system where inter-group movement is important and a greater selectivity in diet than presumed, such forced social distancing and habitat degradation could spell doom.
I saw Phayre’s langurs often during my surveys and was always amazed by their appearance and persistence, having recorded them in the most degraded of habitats. A decade later I sometimes wonder if those small isolated pockets of forest are still home to these wonderfully weird primates.