There are seven species in the genus Hylobates and all are classified as Endangered by the IUCN Red List and are listed on Appendix I of the CITES program, meaning that they are highly endangered and threatened with extinction.

The taxonomy of the gibbons has changed in recent years (Geissmann, 1995). In the past all gibbon species were considered Hylobates but due to different chromosome numbers, cranial shapes and physiology another three genera are classified today. The genus Hylobates now includes seven species that are distributed throughout the whole of Southeast Asia:

• Agile Gibbon (H. agilis, middle and eastern Sumatra, Malay Peninsula)
• Bornean White-bearded Gibbon (H. albibaris, endemic to southwestern Borneo)
• Kloss´s Gibbon (H. klossii, endemic to the Mentawai Islands)
• Lar Gibbon (H. lar, 5 subspecies, Yunnan, eastern Myanmar, Thailand, Malay Peninsula, Sumatra)
• Silvery Javan Gibbon (H. moloch, 2 subspecies, endemic to west and central Java)
• Müller´s Bornean Gibbon (H. muelleri, 3 subspecies, endemic to north and east Borneo)
• Pileated Gibbon (H. pileatus, southeast Thailand, western Cambodia and southwest Laos)

Hylobates have the biggest range of all gibbons, and most prefer tropical rainforest (primary lowland and sub-montane rainforest, mixed deciduous bamboo forest and seasonal evergreen forest).

Population densities of all Hylobates species are decreasing across their range. It is estimated that about 350,000-500,000 individuals remain, but due to the lack of current survey data we only have rough estimations of population density for most species. Estimations for the different species are as follows:

• Agile Gibbon: 4479 individuals in Sumatra + a few thousand in Thailand (O´Brien et al. 2004)
• Bornean White-bearded Gibbon: 19,000 individuals (Buckley, 2004; Buckley et al. 2006)
• Kloss´s Gibbon: 20,000-25,000 individuals (Whittaker, 2005b, 2006)
• Lar Gibbon: 15,000-20,000 individuals in Indonesia, Malaysia and Myanmar, probably extinct in China (Geissmann et al. 2006; Guo & Wang 1995; Lan & Wang 2000; Boonratana 1997)
• Silvery Javan Gibbon: Fewer than 2,500 mature individuals (Nijman 2004; Geissmann & Nijman 2006)
• Müller´s Bornean Gibbon: 250,000-375,000 individuals (Meijaard & Nijman (unpubl. data), cf. IUCN Redlist)
• Pileated Gibbon: Perhaps more than 35,000 in Cambodia, smaller population in Lao PDR, 13,000-14,000 in Thailand (Traeholt et al. 2005; Duckworth et al. 1999; Tunhikorn et al. 1994; Brockelman & Srikosamatara 1993; Phoonjampa & Brockelman unpub. data (cf. IUCN Redlist))

Like all gibbon genera Hylobates are threatened with extinction and IUCN states that the population trend of all Hylobates species is negative. Their classification as “Endangered” indicates a reduction in population size of more than 50% in the last 45 years (3 generations) and also shows that populations are expected to decline further in the near future.

Hylobates are arboreal frugivorous primates and they are therefore extremely dependent on intact closed canopy forests. Reasons for the population decline are similar across species but they differ in severity between populations and locations.

The major threats to the gibbons are deforestation, habitat loss and hunting. Habitat is greatly reduced by deforestation and drainage of swamps; and coffee, oil palm, rubber and other crop plantations are all expanding industries. The rising price of coffee at the end of the 1990´s led to the increased development of coffee plantations and this aggravated the decline of the Agile Gibbon in Sumatra. Agricultural conversion and infrastructural development in general have led to the building of roads, even in protected areas, and also to the creation of new human settlements. Consequently forest clearing takes place, leading to defragmentation and strip building, while simultaneously increasing access for hunters into gibbon habitat. Gibbons are hunted for subsistence and also for illegal trade in the pet market (especially young animals) and this results in a loss of mature individuals, further exacerbating the problem.

Some Hylobates species have been classified as “Endangered” or “Vulnerable” by the IUCN since the 1980´s and all species fall into these categories since the 1990´s. All of the species are protected by national law and are listed in Appendix I of CITES, indicating that they are threatened with extinction and that international trade is prohibited. However, in comparison to other apes the endangered status of the gibbons is widely underrepresented in the media, hence why they are also called the “forgotten Hominidae”.

The protection status of the seven species and their habitats is very different. There are a number of protected areas but not all populations live within these areas and the actual level of protection and law enforcement, especially in remote areas, is questionable (cf. threads). Multiple actions are necessary to halt the decline of the Hylobates populations. Firstly, management of protected areas needs to be improved and conservation activities must be enlarged to control logging (legal and illegal) and development activities in protected areas. Further, better land management should be implemented, for example community based management programs together with educational efforts could help to change the hunting behaviour of local villagers and to better integrate human needs and habitat protection. Gibbon breeding centres have also been suggested as a way to increase population numbers. Survey efforts are also of great importance since one of the current issues is a lack of survey data and reliable population estimates. These data could also be used to help establish public awareness campaigns and inform the broader public about the alarming situation of the Hylobates.

Hylobates occur in the following protected areas:

• AGILE GIBBON: Bukit Barisan NP, Kerinci Seblat NP, Selantan NP, Way Kambas NP (Indonesia), Mudah WR (Malaysia), Hala Bala Sanctuary (Thailand)
• BORNEAN WHITE-BEARDED GIBBON: Bukit Baka, Bukit Baka NP, Ganung Palung NP, Tanjung Puting NP
• KLOSS’S GIBBON: Siberut NP
• LAR GIBBON: Kaeng Krachan NP
• SILVERY JAVAN GIBBON: Ujong Kulon NP
• MÜLLERS BORNEAN GIBBON: Betung-Kerihun NP, Bukit Baka Bukit Raya NP, Kayan Mentarang, Kutai NP, Sungai Wain Protection Forest, Tanjung Puting NP (Indonesia), Lanjak-Entimau Sanctuary, Semongok FR (Malaysia)
• PILEATED GIBBON: Tab Lan NP, Pang Sida NP, Ta Phraya NP, Khao Ang Ru Nai Sancuary, Khao Soi Dao Sanctuary (Thailand), Samkos and Aural Wildlife Sanctuaries, Central Cardamom Protected Forest (Cambodia)

Here is a list of current projects and studies (source: www.gibbons.de):

• Castle-Smith, Emma: Investigation into acoustic variation in Javan Gibbon (Hylobates moloch) vocalisations. Master's thesis, University of Plymouth, England. E-mail: emma.castle-smith@postgrad.plymouth.ac.uk
• Cheyne, Susan M.: Gibbon Behaviour, Feeding Ecology and Sociobiology. The Orangutan Tropical Peatland Project, CIMTROP, Kampus UNPAR, Tanjung Nyaho, Jalan Yos Sudarso, Palangka Raya, Central Kalimantan, Indonesia, 73112. Study Site: Sebangau National Park, Central Kalimantan. Project website: www.orangutantrop.com Project blog: www.outrop.blogspot.com
• Deeming, Laura: Investigating breeding success and longevity of Javan gibbons (Hylobates moloch) in Indonesian institutions. Master's thesis, University of Plymouth, England. E-mail: laura.deeming@postgrad.plymouth.ac.uk
• Gibbon Conservation Alliance and Gibbon Journal (annually since 2005, free download) www.gibbonconservation.org
• Gibbon Conservation Center www.gibboncenter.org
• Gibbon Rehabilitation Project in Phuket, Thailand gibbonproject.org
• Homepage of Yoichi Inoue e.g. behavioral observations on wild gray gibbons (Hylobates muelleri) in northern Borneo and study on the cognitive development of a young white-handed gibbon (H. lar). http://yoichi2003.web.infoseek.co.jp/engljsh.html
• Javan Gibbon Center in Bogor, Indonesia, established since 2003 http://jgcowajawa.blogspot.com
• Mitchell, Katherine: Evaluation of the welfare of the captive population of Hylobates moloch using genetic analysis. Ph.D. thesis, School of Equine and Animal Science, Writtle College, Chelmsford, Essex, U.K. E-mail: 98291095@writtle.ac.uk
• Save Cambodia's Wildlife local Cambodian conservation organisation providing environmental education, awareness and community outreach programs across Cambodia www.cambodiaswildlife.org
• Silvery Gibbon Project www.silvery.org.au