The Javan gibbon is present in 29 forest areas in western Java (Fig. 1). The total population is conservatively estimated at 4100 to 4500 gibbons (Table 1). Although there are a relatively large number of forest fragments with small numbers of gibbons, >95% of the gibbons are in 11 discrete populations of a hundred individuals or more.
The four largest populations are located in Mt Halimun (>800 gibbons), Mt Simpang, Mts Dieng and Ujung Kulon (c. 500-600 gibbons each). The first and the last areas mentioned are gazetted as national parks and have some basic management facilities in place. Mt Simpang is a strict nature reserve without any facilities or wardens, with protection being restricted to sign posts demarcating the borders, whereas Mts. Dieng is largely unprotected. Half of the 15 largest populations, representing about a third of the total wild population of Javan gibbons, are found in forest areas outside the protected area network.
Eight out of 14 zoological gardens surveyed had one or more Javan gibbons on display, with a combined total of 56 individuals. Many of these were held either in solitary confinement or in large (non-family) groups, often comprising of more than one species of gibbon. In most zoos housing conditions were extremely poor, especially when set against western standards, with the exception of the recently opened Schmutzer Primate Centre in Jakarta and, at least for Javan gibbons, Bali Zoo Park near Denpasar and Taman Safari Indonesia in Cisarua. These three zoos were also the only that maintained at least part of their Javan gibbons in pairs, in such conditions that they could potentially produce offspring. Concerning the origin of the Javan gibbons in these zoos, from 12 this was either unknown or I was unable to trace it, 15 were transferred from other zoos within Indonesia, 24 were donated by the public, and three were confiscated by wildlife conservation authorities (though none of the owners prosecuted). All but two were wild-caught, and for the two that were allegedly captive-bred, insufficient reliable information was available to assess whether this was indeed the case. To the best of my knowledge Javan gibbons have not reproduced successfully in any of these Indonesian zoos.
In four wildlife rescue centres there were 15 Javan gibbons, seven of which were confiscated (again, none of the owners were prosecuted) and eight were donated by the public. Despite best efforts, housing conditions in most of the wildlife rescue centres, although often considerably better than in zoos, are not up to western standards, and most individuals were kept solitary. With the exception of four Javan gibbons donated to the Javan Gibbon Rescue and Rehabilitation Centre at Bodogol in 2003, at least at the moment, none of these gibbons are intended to participate in a breeding programme. As such, as of 2004 there are at least 70 Javan gibbons in Indonesian institutions, of which there is a maximum of five potential breeding pairs, and no definite proof of successful breeding.
After 1978 (when Indonesia acceded to the CITES) at least nine wild-caught Javan gibbons were exported from Indonesia to foreign zoos. Outside Indonesia there are 48 Javan gibbons at ten institutions in nine countries. Three of these institutions have successfully bred the species, with some six breeding pairs. At least 60% of the Javan gibbons outside Indonesia are captive-bred. As such, the global ex-situ population of the Javan gibbon falls just short of 120 individuals at 22 institutions in ten countries; the majority of these are wild-caught and do not form part of a breeding programme.