Status review of gibbons in Vietnam

Thomas Geissmann¹, Nguyen Xuan Dang², Nicolas Lormée² & Frank Momberg²

¹ Anthropological Institute, University Zurich-Irchel, Winterthurerstrasse 190, CH - 8057 Zurich, SWITZERLAND
² Fauna & Flora International, Asia Pacific Programme, Hanoi, VIETNAM

This section has been published as:
Geissmann, T.; Nguyen Xuan Dang; Lormée, N. & Momberg, F., 2003: Status review of gibbons in Vietnam. Asian Primates 8(3-4): 10-12.

A printable pdf-file of this paper can be downloaded here.

Although several faunistic surveys have been carried out in Vietnam in recent years, survey results have rarely been published. Research results, too, are often preliminary reports published in little-known local journals. A critical reassessment of the gibbon populations, their size and their phylogenetic affinities is urgently required.

The Vietnam Primate Conservation Status Review began implementation in July 1999 with the objective of collating a comprehensive data set for leaf monkeys and gibbons. The results on gibbons have recently been published (Geissmann et al., 2000). This is not only the first nation-wide status review of Vietnamese gibbons, but also the first scientific book publication on gibbons in several years. An edition in the Vietnamese language has also been published. The present text is a short summary of the most interesting findings of the status survey.

Recent research results suggest that the diversity of Indochinese gibbons is larger than previously assumed. All Vietnamese gibbons are members of the genus Nomascus (crested gibbons). Based on a preliminary analysis of tape-recorded gibbon songs, the affinities of populations in a large area in central Vietnam, southern Laos and possibly northeastern Cambodia appear to be particularly complex. This area may either represent a transition zone between what is usually identified as N. leucogenys siki and N. gabriellae, or it may include a previously undescribed taxon. In order to test either hypothesis, we strongly recommend that field surveys be carried out throughout this area which should tape-record gibbon songs at different latitudes. For the present status report, gibbons from this area have been analysed separately.

Based on earlier reports, museum specimens or forest quality, we were able to identify 87 potential gibbon areas in Vietnam (Table 1). During the last 5 years, however, the occurrence of gibbons was only confirmed for 21 of these areas. In 17 additional areas, the occurrence of gibbons is probable, albeit not reliably documented. In 49 areas (56.3%), gibbons are possibly or probably extinct. The proportion of these areas is particularly high in northern Vietnam: Nomascus concolor 61.1%, N. leucogenys leucogenys 74.1%, and N. sp. cf. nasutus 75%.

Table 1. Status of crested gibbons at known or suspected gibbon loccalities in Vietnam and numbers of localities surveyed. The table lists numbers of localities and (in parentheses) their proportion relative to the total number of known localities for each taxon.

The situation is particularly alarming for N. sp. cf. nasutus which had no reliably confirmed populations in Vietnam (12 localities evaluated) until this status survey was finished, in spite of several field surveys which were specifically carried out in order to find this species (e.g. Geissmann and Vu Ngoc Than, 2001). At the time of our status report, the only confirmed observations of this species were made on the Chinese island of Hainan (population: less than 20 individuals). Only more recently, a small surviving population of this taxon was discovered (Geissmann et al., this issue), but the Vietnamese population is so small (less than 30 individuals) that this species still appears to exhibit the sad distinction of not only being the most critically endangered ape species but also the most critically endangered primate species of the world.

Other gibbons in the northern half of Vietnam are also critically endangered: N. concolor was confirmed in only two of 18 localities, and N. leucogenys leucogenys in only four of 27. This comes particularly surprising for the latter taxon which is relatively frequently encountered in zoos and animal markets, both in Vietnam and neighboring countries.

On the positive side, field surveys carried out by FFI throughout most of the remaining larger forest ares in the historic range of N. concolor lead to the discovery of several remnant populations, the two largest appear to live in Che Tao and Ho Nam Mu forests (Yen Bai and Lao Cai provinces) with about 70 and 20 individuals, respectively. Yet, the total estimate of the species is less than 100 individuals for Vietnam.

Appendix 1 in the status review lists the occurrence of the various gibbon taxa in the protected area network of Vietnam. The proportion of protected areas that contain confirmed populations of gibbons ranges from 0% for both N. sp. cf. nasutus and N. concolor, 40% for both N. gabriellae, and the population located between siki and gabriellae, 50% for N. leucogenys leucogenys, to 100% for N. leucogenys siki.

References

Geissmann, T.; La Quang Trung; Trinh Dinh Hoang; Vu Dinh Thong; Dang Ngoc Can & Pham Duc Tien (2003). Rarest apes species rediscovered in Vietnam, with special reference to gibbons. Asian Primates 8 (3&4): 8-9.

Geissmann, T.; Nguyen Xuan Dang; Lormée, N. & Momberg, F. (2000). Vietnam primate conservation status review 2000 - Part 1: Gibbons. English edition. Fauna & Flora International, Indochina Programme, Hanoi. 130 pp. ISBN: 1-903703-03-4. *

Geissmann, T. and Vu Ngoc Thanh (2001). Preliminary results of a primate survey in northeastern Vietnam, with special reference to gibbons. Asian Primates 7(3&4): 0-4.

* Available from: Fauna & Flora International, Asia Pacific Programme Office, IPO Box 78, 55 To Hien Thanh, Hanoi, Vietnam, Fax: +84-4 978 44 40, E-mail: primates@ffi.org.vn or vietnam@ffi.org.vn

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