Wildlife of Lao PDR: 1999 Status Report - IUCN

[• Hylobates gabriellae Yellow-cheeked Crested Gibbon
(= Buff-cheeked Gibbon; = Yellow-cheeked Gibbon; = Redcheeked
Gibbon; = Golden-cheeked Gibbon); (included in
H. concolor Crested Gibbon M4 ; one form treated as a race of
this species M5 is classified here under H. leucogenys)]. Conservation
Significance: Data Deficient (Global); Little Known
in Lao PDR; CITES Appendix I. Endemic to far southern
Lao PDR(?), southern Vietnam and eastern Cambodia;
occurs only east of the Mekong (Geissmann 1995). Context:
The species may occur in Lao PDR south from the Bolaven
Plateau to the Cambodian border (Geissmann 1995), but information
is conflicting. Tape-recordings from Xe Pian
NBCA in 1993 showed some characters of siki, even though
museum specimens from the Bolaven Plateau, to the north,
look like H. gabriellae (Geissmann 1995). Recently-taped
songs from the Bolaven Plateau also show features of H. l.
siki (T. Geissmann in litt. 1999). Male gibbons observed in
Nam Ghong Provincial PA and Dong Ampham NBCA in
1997-1998 resembled H. gabriellae in pelage (RJTiz, JAW)
but cannot be considered certainly identified. Males from Xe
Bang-Nouan NBCA, well north of the Xe Pian / Bolaven
Plateau population, also show features of H. gabriellae
(RJTim). Pure H. gabriellae are only likely to occur in the
far south, if they occur in Lao PDR at all, and should only be
identified by song. Deuve’s (1972) claim of sympatry with
Pileated Gibbon in Champasak Province is insupportable. The
presentation of information in Duckworth et al. (1994, 1995)
as referring to H. gabriellae ssp. was based on Corbet and
Hill’s (1992) taxonomy, taking siki as a subspecies of
gabriellae. Taxonomic issues: See notes under H. concolor
and H. leucogenys.
Status Information on Pale-cheeked Nomascus gibbons: Identification
criteria for field use between the three forms
leucogenys, siki and gabriellae are evolving. Under typical
viewing conditions in Lao PDR, visual field identification is
likely to be possible only rarely. The main technique will
remain sonographic analysis of tape-recorded calls
(Geissmann 1995). Few calls have yet been analysed fully,
thus the status of individual pale-cheeked gibbon taxa in Lao
PDR remains unclear (Plate 13).
Gibbons were reported in 89% of 1988-1993 village interviews
(n = 328), from across Lao PDR (Annex 5). All
those east of the Mekong are likely to be Nomascus, and all
those outside a limited area of the north-west are likely to be
pale-cheeked forms. The few direct sightings of gibbons in
the north make it difficult to define the area occupied by palecheeked
forms, but Nam Xam, Nam Et and Phou Louey
NBCAs are all known to support them.
Gibbons have been found widely (Table 12), from the
Mekong plains up to at least 1550 m in the Phou Ahyon area,
1650 m in Phou Louey NBCA, and 1800 m in Nakai-Nam
Theun NBCA (Timmins and Vongkhamheng 1996a,
Davidson 1998, Evans et al. in prep. b). Davidson et al. (1997)
Large Mammals
and Showler et al. (1998a) discussed the possibility of close
co-occurrence of white-cheeked and buff-cheeked animals
in south-east Lao PDR, re-emphasising the need for caution
in field identification of pale-cheeked forms using morphological
criteria. Currently at no site has the intra-population
variation in male cheek pelage features and song characteristics
been documented.
Gibbons are hunted and eaten avidly in the central
Annamites (WGR; Plate 5), but other villagers reportedly
avoid hunting them. They were not reported as a major food
species during 1988-1993 interviews (Table 1). Gibbons are
kept as pets in Lao PDR (Bergmans 1995, Duckworth et al.
1995; Plate 13), and Lao gibbons reportedly can be ordered
from wildlife dealers operating in Thailand (Srikosamatara
et al. 1992, Baird 1993). There is some market hunting, in
which females are shot to collect their young for sale to foreign
and perhaps Lao buyers. Gibbons are heavily traded with
Vietnam (e.g. Davidson et al. 1997, Compton in prep. b).
In many areas, e.g. Phou Xang He and Dong Hua Sao
NBCAs, gibbons are patchily distributed and seem to be
absent across logged or fragmented forest, either as a result
of habitat destruction or hunting and other forms of human
disturbance (Duckworth et al. 1995). These factors are probably
reducing numbers in all encroached forest in Lao PDR.
Although Evans et al. (1996b) found small numbers in some
areas of Dong Hua Sao NBCA where Duckworth et al. (1995)
had predicted them (on the basis of habitat) to be absent, the
general conclusion, that numbers were severely depressed in
encroached areas, was supported. Where protection from
hunting is having some effect (e.g. Sangthong District), gibbons
can persist in heavily degraded areas, suggesting that
decreases in the other areas reflect primarily hunting pressure
rather than the habitat being totally unsuitable
(Duckworth 1996a).
In Xe Pian NBCA gibbons occur at high densities in primary
semi-evergreen forest, in both flat and hilly areas. The
large Xe Pian-Dong Hua Sao NBCAs population is of major
global significance for gibbon conservation, particularly as
it may lie along a zone of contact between H. l. siki and H.
gabriellae (Duckworth et al. 1995, Geissmann 1995). The
extensive forested parts of the Nam Theun catchment
(notably Nakai-Nam Theun NBCA) support a population of
equally high global significance, which is likely to be
taxonomically different from that in the south (Evans et al.
in prep. b). North of the Nam Theun catchment, gibbons are
rarer than to the south. Surveys in 1997-1998 across the
NBCAs of north Lao PDR found large populations only in
Nam Xam NBCA and parts of Phou Louey NBCA. Indeed,
in some areas there were no direct records of gibbons: Nam
Ha NBCA (where they appear to have been hunted out; M.
Meredith verbally 1999) and Phou Dendin NBCA (where
effort has been insufficient to speculate on status). The palecheeked
gibbons in Lao PDR are of major global significance,
as populations in Vietnam and China have been
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