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Population abundance and distribution of the endangered golden langur (Trachypithecus geei, Khajuria 1956) in Bhutan

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Abstract

Reliable population estimates are lacking for many South Asian primate species, including the golden langur (Trachypithecus geei), which is endangered and restricted to Bhutan and northeast India. Although well studied in India, few studies exist on this species in Bhutan. In November 2017, we undertook a nationwide survey of golden langurs in Bhutan using double observers along trail-based transects in 17 blocks within its habitat, and modeled its distribution using MaxEnt. A total of 2439 golden langurs in 222 groups were collectively encountered by 17 teams of double observers, from which, an overall population of 2516 ± SE 363 individuals and 236 ± SE 9 groups were estimated. Group sizes varied from 2 to 35 individuals with a mean of 11 ± SD 0.38 individuals. A total of 468 adult males (19%), 924 adult females (38%), 649 juveniles (27%), and 398 infants (16%) were counted. Adult male-to-female sex ratio was 1:1.97 and adult female-to-infant ratio was 1:0.43. We determined 2848 km2 of suitable area for golden langurs in Bhutan and estimated a density of 0.88 individuals/km2. Our population estimate of golden langurs in Bhutan is much lower than the current IUCN estimate of 4000 individuals for Bhutan, necessitating a reassessment of its current conservation status due to threats from road kills, electrocution, and development activities like road construction, hydropower, and electrical transmission lines. We further recommend our refined double-observer survey method to reliably estimate primate populations in rugged terrain.

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Photo credit: Kado Rinchen, Langthel Range, Jigme Singye Wangchuck National Park

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Acknowledgements

We thank the Royal Government of Bhutan for administrative approval and funding for the study and the Mangdechhu Hydropower Project Authority for supplemental funding. We acknowledge field efforts and diligence of other observers nominated from Tsirang Division (Cheten Dorji), Sarpang Division (R. B. Mongar, Sangay Dorji, and Rinzin Wangchuk), Zhemgang Division (Kezang Dorji and Tshering Dorji), Bumthang Division (Sonam Rinzin and Dorji Thinley), Jigme Singye Wangchuck National Park (Namgay Dorji, Cheku, Tshering, Sanjit Kumar Rai, Kado Rinchen, and Pema Namgyel), Royal Manas National Park (Chhimi Tshewang, Tshering Tashi, Jamphel Lhendup, Sangay Tenzin, Dambar Bahadur Chhetri, Deo Kumar Gurung, Ngawang Namgyal, and Sonam Dorji), and Phibsoo Wildlife Sanctuary (Tendel Wangdi, Karma Chedup, Tshewang Tenzin, and Tshering Wangdi). We thank Phento Tshering, the former Director of the Department of Forests and Park Services and Shacha Dorji, Director of the Ugyen Wangchuck Institute for Conservation and Environment Research, for administrative approval and the Chief Forestry Officers (Dimple Thapa, Pankey Dukpa, Phub Dhendup, Singye Wangmo, Dorji Rabten, Kinzang Gyeltshen, and Tashi Dendup), Program Director (Kaka Tshering), and the Range Officers of JSWNP (Phuntshok and Yeshey Wangdi) for their critical support and cooperation during the surveys and preliminary visits.

Funding

Funding received from Royal Government of Bhutan (FY 2017–2018) and Mangdechhu Hydropower Project Authority (FY 2017–2018).

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Authors and Affiliations

  1. Ugyen Wangchuck Institute for Conservation and Environment Research, Department of Forests and Park Services, Lamaigoenpa, Bumthang, 32001, Bhutan

    Phuntsho Thinley, Tshewang Norbu & Kezang Wangchuk

  2. Geography and Planning, University of New England, Armidale, NSW, 2351, Australia

    Rajanathan Rajaratnam

  3. Ecosystem Management, University of New England, Armidale, NSW, 2351, Australia

    Phuntsho Thinley & Karl Vernes

  4. Sarpang Forest Division, Department of Forests and Park Services, Sarpang, 31002, Bhutan

    Karma Choki, Jigme Tenzin & Sangay Tenzin

  5. Tsirang Forest Division, Department of Forests and Park Services, Tsirang, 36001, Bhutan

    Kinley, Shacha Dorji, Tshering Wangchuk, Karma Cheda &  Gempa

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  1. Phuntsho Thinley
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  2. Tshewang Norbu
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Correspondence to Phuntsho Thinley.

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Thinley, P., Norbu, T., Rajaratnam, R. et al. Population abundance and distribution of the endangered golden langur (Trachypithecus geei, Khajuria 1956) in Bhutan. Primates 60, 437–448 (2019). https://doi.org/10.1007/s10329-019-00737-w

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