Providing evidence to improve practice

Individual study: A glut of gibbons in Sarawak – is rehabilitation the answer?

Published source details

Bennett J. (1992) A glut of gibbons in Sarawak – is rehabilitation the answer? Oryx, 26, 157-164


This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.

Reintroduce primates into habitat where the species is absent Primate Conservation

A before-and-after trial in 1976–1988 in a degraded tropical forest in Sarawak, Malaysia found that at least 77 of 87 (89%) captive, wild-born Müller's Bornean gibbons Hylobates muelleri that were reintroduced into habitat without resident wild gibbons along with other interventions, died after release. Confiscated gibbons had undergone veterinary checks and were placed in holding cages in a forest clearing. When possible, males and females were paired in cages prior to release. Müller's Bornean gibbons were protected under state law. Surveys of direct sightings and gibbon calls were conducted simultaneously by three or four observers on non-rainy days on eight mornings from 4 February to 31 March 1988. The study does not distinguish between the effects of the different interventions mentioned above.

Conduct veterinary screens of animals before reintroducing/translocating them Primate Conservation

A before-and-after trial in 1976-1988 in a degraded tropical forest in Semenggoh Forest Reserve, Malaysia (2) found that at least 77 of 87 (90%) reintroduced captive, wild-born Müller's Bornean gibbons Hylobates muelleri that underwent veterinary checks before release along with other interventions, did not survive after release. Confiscated gibbons were placed in holding cages in a forest clearing for an unknown amount of time prior to release. Where possible, males and females were paired in cages before release into habitat without resident gibbons. Müller's Bornean gibbons were fully protected under the Wild Life Protection Ordinance in Sarawak. Surveys of direct sightings and gibbon calls along grid squares (500 x 500 m) covering a total of 9.5 km were conducted simultaneously by 3-4 observers on non-rainy days on eight mornings in February-March 1988. The study does not distinguish between the effects of the different interventions mentioned above.

Implement legal protection for primate species under threat Primate Conservation

A before-and-after trial in 1976-1988 in a degraded tropical forest in Semenggoh Forest Reserve, Malaysia found that at least 77 of 87 (90%) reintroduced captive, wild-born Müller's Bornean gibbons Hylobates muelleri that were legally protected in the area along with other interventions, did not survive after release. Müller's Bornean gibbons were fully protected under the Wild Life Protection Ordinance in Sarawak that also forbade keeping gibbons as pets. Confiscated gibbons had undergone veterinary checks and were placed in holding cages in a forest clearing for an unknown amount of time. Where possible, males and females were paired in cages prior to release into habitat without wild resident gibbons. Surveys of direct sightings and gibbon calls along grid squares (500 x 500 m) covering a total of 9.5 km were conducted simultaneously by three or four observers on non-rainy days in February-March 1988.  The study does not distinguish between the effects of the different interventions mentioned above.

Reintroduce primates as single/multiple individuals Primate Conservation

A study, which was included in a review, in 1976–1977 in dry evergreen forest in Thailand on captive lar gibbons Hylobates lar that were partially released as single or multiple individuals, along with other interventions, found that their population decreased by 6% and no infants were born in the first 17 months after release. No statistical tests were carried out to determine whether this decrease was significant. Four gibbons joined wild groups. A total of 31 gibbons were introduced as individuals, pairs, or family groups into habitat with resident wild gibbons. Anaesthetized gibbons were either kept in separate cages for 14 days before release, or laid on the forest floor. Injured animals were recaptured and treated. In 1961, gibbons were officially protected by the Thai government. The study does not distinguish between the effects of the different interventions mentioned above.

Allow primates to adapt to local habitat conditions for some time before introduction to the wild Primate Conservation

A before-and-after trial in 1976-1988 in degraded tropical forest in Semenggoh Forest Reserve, Malaysia found that at least 77 of 87 (90%) reintroduced captive, wild-born Müller's Bornean gibbons Hylobates muelleri that were allowed to adapt to local habitat conditions for some time before reintroduction along with other interventions, did not survive after release. Confiscated gibbons had undergone veterinary checks and were placed in holding cages in a forest clearing for an unknown amount of time. Some individuals were released within days of being received at the sanctuary. When possible, males and females were paired in cages prior to release into habitat without resident wild gibbons. The species was fully protected in Sarawak. Surveys of direct sightings and gibbon calls along grid squares (500 x 500 m) covering a total of 9.5 km were conducted simultaneously by three or four observers on non-rainy days on eight mornings in February-March 1988. The study does not distinguish between the effects of the different interventions mentioned above.