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Appearance

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The Phayre’s langur is characterized by white coloration around the ventral, mouth, and eye area. The broad ring-shaped patches around the eyes resemble spectacles, contributing to the local name of “Chasma bandor” in Bengali, or spectacled monkey. The white fur is especially contrasting with the overall deep bluish-brown fur all over its body with darker shades at the head, below the elbows, and at the end of the tail[1]. There is a presence of a sagittal crest on the heads of both adult males and females, giving it a triangular shape. The infants have a straw-colored natal coat, making it easily distinguishable in a group[2]. The average head-body length ranges from 530-580 mm in males and 495-580 mm in females. The tail is usually longer in that its body, with an average of 700 mm for males and 750 mm, for females.  In comparison to T. melamera and T. popa, it has a shorter tail length. The average mass of Phayre’s langur is observed to be around 7.9 kg for males and 6.9 kg for males[3].

In field studies males and females are differentiated through the shape of the patches around the eyes. The female monkeys have cone-shaped white patches bending in towards the nose while the males have a rounder shape. The shape difference causes a slightly wider gap in males than in females[4].

Like most Old-world monkeys, it has the dental formula of 2:1:2:3[5]. Distinctive to other colobines Phayre’s langur show craniodental adaptations such as medially positioned rows of teeth and stronger masseter pterygoid muscles, for seed-eating[6].

Behavior

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Group Structure

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The Phayre’s langur usually forms multi-male and multi-female with a presence of a dominant male alpha in the group[7][3]. All-male groups, one-male groups, and one-female groups have also been observed though, less common. A high level of territoriality is seen within the species and between groups. The groups tend to maintain occupancy in their home range, showing philopatry[3]. Foraging is done by maintaining groups throughout different ranges.  While foraging, groups tend to avoid ranging areas of neighboring groups suggesting the formation of borders between them, agonistic interactions are observed in places of overlapping borders[8][3].

Female dispersal is also observed between the groups, females that leave the group tend to obtain alpha rank in the new group. Linear dominance is seen in females, where rank has a linear relationship with age[9][10]. Males on reaching maturation show some dispersal, they either form new multi-male groups or return to their natal group. For males, age and rank dominance also show a linear relationship though, the ranks can change depending on the resource-holding potential, which is shown to decrease in aging monkeys[7].

Reproduction

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Female Phayre’s langurs are pregnant by an average age of 5.3 years with an average gestation period of 205 days[11]. The females show promiscuous behavior, studies do show a preference for more experienced males, usually of higher dominance. Polygynous relationships are common, where males offer protection to copulated females[7].

Females usually nurse their infants on average 22 months with weaning at around 19-21 months. The natal coat starts to become darker 26 weeks after birth[12].

Communication

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Vocalization is observed in both males and females. Based on observations in the wild, a loud “kah-kah-kah” is used to sound alarm in the troop, while in the presence of a predator a softer “whoo” call is used[9]. The dominant male alpha uses the “cheng-kong” sound to assemble the group. Additionally, vocalization essential is for maintaining contact with troop members while foraging. In agonistic interactions, barking sounds such as “ngre-go, ngre-go” are used to maintain their group's territory[1][3].

Ecology

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The Phayre’s Leaf Monkey is diurnal and arboreal. The average life span of the Phayre’s leaf Monkey is 20-30 years, in the wild, and an average of 28.3 in captivity[3].

Activity Budget

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A study conducted in the Satchari National Park, Bangladesh, found on average the Phayre’s leaf Monkey spends, most of its time foraging and feeding (40.7%), the rest is spent traveling (31.8%), resting (18.3%), grooming (7.8%) and playing (1.4%)[13]. It is seen that males and juveniles tend to spend more time moving than adult females, who also have the highest percentage of resting among them. It is noticed that the activity patterns have variations based on habitats, seasons, and food availability, for example, food shortages lead to increased travel time. The variation in caloric content of different foods have shown to affect the energy budgets, i.e., poor quality food leads to higher feeding distribution to maintain the caloric requirements[3][13].

Diet

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The Phayre’s leaf monkey is a folivore. It feeds on leaves, shoots, seeds, flowers, gum, and fleshy parts of fruits. The diet varies between seasons and different regions, showing adaptation to the local flora.

In a study conducted in Dampa Tiger Reserve, Mizoram, India, the Phayre’s langurs during summer can be seen feeding on Citrus grandis, Gmelina arborea, Ficus maclellendii, Buetneria Pilosa, with a preference towards bamboos such as Musa ornata, Melocana baccifera, and Dendrocalamus longispathus[14]. Plant parts with less fiber and high proteins and sugars such as young leaves are usually preferred while foraging[3]. In the Stachari National Park in Bangladesh, Ficus hispida, Albizia chinensis, and Vachellia nilotica have the highest consumption[13].

The high bamboo consumption in their diets is attributed to the abundance of this plant in North-East India because of its invasive nature[15]. The Phayre’s langur living in local rubber plantations in Mizoram majorly consume leaves of Hevea brasiliensis (Rubber tree)[3], showing that diet is affected by the plant diversity in its home range.

Habitat and Distribution

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The Pharye’s langur is found in tropical, deciduous, and evergreen forests of North-East India, Eastern Bangladesh, and Western Myanmar. It can also be seen residing in secondary forests such as bamboo clusters and rubber plantations. Tree species with large canopies like Artocarpus chaplasha, Artocarpus lakoocha, Ficus racemosa, Trophis aspera, Mangifera indica, and Grewia nervosa, in Bangladesh, are used for resting their shade[13]. In India, the most common roosting trees range from heights 6-15m and have an extensive canopy, e.g., Ficus hispada and Sapium sebifera in Mizoram[3]. Currently, a total of 1200 individual langurs have been recorded in India and 376 individuals in Bangladesh[16], 288 of which resided in the northeastern forest of Bangladesh[17].

Conservation

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The IUCN has deemed the population of Phayre’s langur to be decreasing. The recent reclassification of Phayre’s langur has led to the underestimation of the status of the decline in the specie’s population. It is also listed in the CITES Appendix II, to protect its illegal poaching and trading locally. The major threats to Phayre’s langur are habitat destruction, fragmentation, logging, roadkill, ecotourism, electrocution, and hunting.

In India, organizations like the Wildlife Trust of India have employed wildlife staff trained in anti-poaching tactics to work in forests, and locals have also been involved[9]. In Bangladesh, 'Phayre's Langur Conservation Initiative', a project was started by a local NGO[18] to assess the population status and threats to Phayre’s langur. In both India and Bangladesh, Pharye’s langur is protected through local legislation for implementing international conservation law.

The 'jhooming’, a form of shifting cultivation practiced by tribes in India, led to concerns over reducing forestland for the Phayre’s langur population, but a study showed that they adapted to the local practice. The regenerating secondary forests through ‘jhooming‘ provide a habitat for the langurs when primary forests are affected due to anthropogenic factors[19].

  1. ^ a b Choudhray, A. (2001). A systematic review of the mammals of North-East India with special reference non-human to primates. Gauhati University (India) ProQuest Dissertations Publishing,  2001. 10116542.
  2. ^ Alley, T.R. Infantile colouration as an elicitor of caretaking behaviour in old world primates. Primates 21, 416–429 (1980). https://doi.org/10.1007/BF02390470
  3. ^ a b c d e f g h i j Bose,J., (2005), An Ecobehavioural Study of Phayre's leaf monkey Trachypithecus phayrei (Blyth, 1847). Gauhati University (India) ProQuest Dissertations Publishing,  2005. 10116537.
  4. ^ Bhattacharya, T., Chakraborty, D.(1990). Sex identification of the phayre's leaf monkey (Presbytis phayrei BLYTH, 1847) with the help of facial marks. Primates 31, 617–620. https://doi.org/10.1007/BF02382547
  5. ^ Ankel-Simons, F. (2007).Chapter 7 - Teeth, Primate Anatomy (Third Edition), Academic Press, Pages 223-281. ISBN 9780123725769. https://doi.org/10.1016/B978-012372576-9/50009-7
  6. ^ Koyabu, D. B., & Endo, H. (2010). Craniodental mechanics and diet in Asian colobines: Morphological evidence of mature seed predation and sclerocarpy. American Journal of Physical Anthropology. https://doi.org/10.1002/ajpa.21213
  7. ^ a b c Koenig, A., Borries, C. (2011). Social Organization and male residence pattern in Phayre’s leaf monkeys. Long-Term Field Studies of Primates, 215–236. https://doi.org/10.1007/978-3-642-22514-7_10
  8. ^ Gibson, L., & Koenig, A. (2012). Neighboring groups and habitat edges modulate range use in Phayre’s leaf monkeys (Trachypithecus phayrei crepusculus). Behavioral Ecology and Sociobiology, 66(4), 633–643. http://www.jstor.org/stable/41501760
  9. ^ a b c Wildlife Institute of India. (2018). National Studbook of Phayre's leaf monkey (Trachypithecus phayrei): II Edition, Wildlife Institute of India, Dehradun and Central Zoo Authority, New Delhi.
  10. ^ Lu, A., Beehner, J.C., Czekala, N.M. and Borries, C. (2012), Juggling Priorities: Female Mating Tactics in Phayre's Leaf Monkeys. Am. J. Primatol., 74: 471-481. https://doi.org/10.1002/ajp.22004
  11. ^ Lu, A., Beehner, J.C., Czekala, N.M. and Borries, C. (2010). Reproductive characteristics of wild female Phayre’s leaf monkeys. Am J Primatol 72:1073–1081https://doi.org/10.1002/ajp.20866
  12. ^ Borries, C., Lu, A., Ossi-Lupo, K., Larney, E., Koenig, A. (2004).The meaning of weaning in wild Phayre's leaf monkeys: last nipple contact, survival, and independence. Am J Phys Anthropol. Jun;154(2):291-301. doi: 10.1002/ajpa.22511. Epub 2014 Mar 11. PMID: 24615436.
  13. ^ a b c d Naher, H., Mondal, T., Hasan, S., Muzaffar, S., Khan, S. (2022). Activity Budget and Diet of Phayre's Langur (Trachypithecus phayrei) in Satchari National Park, Bangladesh. Primate Conservation. 36. 1-17.https://www.researchgate.net/publication/359035744_Activity_Budget_and_Diet_of_Phayre's_Langur_Trachypithecus_phayrei_in_Satchari_National_Park_Bangladesh
  14. ^ Parida, A., Solanki, G., Decemson, Ht. (2018). Feeding Behavior of Phayre’s Leaf Monkey (Trachypithecus phayrei) and Capped Langur (Trachypithecus pileatus) in Dampa Tiger Reserve, Mizoram. Science & Technology Journal. 6. 31-38. https://www.researchgate.net/publication/327690948_Feeding_Behavior_of_Phayre's_Leaf_Monkey_Trachypithecus_phayrei_and_Capped_Langur_Trachypithecus_pileatus_in_Dampa_Tiger_Reserve_Mizoram
  15. ^ Majumdar, K., Nath, A. J., Gupta, A. K., & Datta, B. K. (2015). Bamboo invasion: threat to primate conservation in North East India. Current Science, 108(11), 1969–1971. http://www.jstor.org/stable/24905551
  16. ^ Chetry, D. & Ahmed, T. 2021. Trachypithecus phayrei. The IUCN Red List of Threatened Species 2021: e.T175862145A175862149. https://dx.doi.org/10.2305/IUCN.UK.2021- 2.RLTS.T175862145A175862149.en
  17. ^ Ahmed, T., Hasan, S., Nath, S., Biswas, S. (2019). Phayre’s Langur Population in Northeast Bangladesh: Underestimated and Under-pressure. https://www.researchgate.net/publication/336722104_Phayre's_Langur_Population_in_Northeast_Bangladesh_Underestimated_and_Under-pressure
  18. ^ Ahmed, T., (n.d.). National Conservation Management, Bangladesh. https://wildprimate.wordpress.com/research/
  19. ^ Gupta, A. K. (2000). Shifting Cultivation and Conservation of Biological Diversity in Tripura, Northeast India. Human Ecology, 28(4), 605–629. http://www.jstor.org/stable/4603374
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