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Order : PRIMATES
Family : Cercopithecidae
Species : Presbytis siamensis rhionis
Head-body length : approx. 50 cm ?
Tail length : approx. 70 cm ?
Weight : maximum approx. 6.5 kg ?
Play
alarm call of P. s. rhionis ►
Presbytis siamensis
(White-thighed Surili) is taxonomically divided into 4 subspecies, each of
which occurs in separate geographical areas of southernmost Thailand, Peninsular Malaysia and
Indonesia (eastern Sumatra and the Riau Archipelago) (Ang & Traeholt,
2020).
Presbytis siamensis rhionis (Bintan Island Pale-thighed Langur) is a
subspecies known only from the island of Bintan, in the northeastern
part of the Riau Archipelago, 35 km southeast of Singapore (Ang et al,
2020); potentially it might also occur on the islands of Batam and Galang, to the west of
Bintan. This subspecies is listed as Endangered.
The diet of Presbytis siamensis as a whole comprises young leaves,
flowers, fruits and seeds. This primate is almost exclusively arboreal, but
they may
descend to the ground to quickly move between adjacent areas of woodland.
Group size typically comprises 8 individuals or less.
The known habitats of the 3 subspecies of Presbytis siamensis which occur in
Indonesia include primary forest, secondary forest, swamp forest, rubber
tree plantations and mangrove (Supriatna, 2019).
Bintan Island supports extremely degraded habitats, as a result of
historical deforestation (often for gambier), agriculture, mineral extraction
(bauxite), urban development and tourist facilities. Increasingly
oil palm is being planted on degraded habitats. Little lowland primary
forest remains, however mangrove ecosystems appear more intact; ongoing
research may determine to what degree
Presbytis siamensis rhionis utilises mangrove habitat.
The fur of this rather shy primate is brown dorsally and grey ventrally. The face is brown with pale
markings, and the hands and feet are blackish. The alarm call, typically
emitted by a dominant male, is similar to that of
other Presbytis.
Local people on Bintan Island refer to this primate as 'kera cantik' (=
'beautiful ape') or 'kekah' (Supriatna, 2019). It is also referred to as 'Bila',
which is an acronym formed from the first two letters of the words 'Bintan'
and 'langur'.
Figs 1 and 2 : Female and infant on Bintan Island, Indonesia. Photos thanks
to Dirga Priyambada.
Fig 3 : Image from November 2007 of a lone individual seen running across a
rural road in the central part of Bintan Island, between fragments of secondary forest.
Fig 4 : View of Gunung Bintan Kecil, an isolated remnant of intact lowland
forest, surrounded by sparse secondary forest and secondary scrub.
Fig 5 : Tall trees on a forested ridge near the tourist golf course at Ria
Bintan. Such habitats, if properly protected
and enhanced, may provide a refuge for this endangered species in the north of Bintan
Island.
References :
Ang, A. & Traeholt, C. 2020. Presbytis siamensis. The IUCN
Red List of Threatened Species 2020: e.T18134A17953755.
Ang, A., Cheyne, S. & Traeholt, C. 2020. Presbytis siamensis ssp.
rhionis. The IUCN Red List of Threatened Species 2020:
e.T39825A17986328.
Supriatna, J. (2019). Field Guide to the Primates of Indonesia. Yayasan
Pustaka Obor Indonesia. 233 pp.
Acknowledgments : Audio file courtesy Yong Ding Li. Thanks to Dirga Priyambada for generously
sharing his images. |
