In the forest

Re – Introduction


Re-introduction methods

The Gibbon Rehabilitation Project is the longest running gibbon reintroduction project in the world. Following unsuccessful early attempts at reintroduction in the 1990’s GRP has developed a specific method for gibbon reintroductions that has led to the establishment of an independent small, breeding population of captive raised gibbons now surviving on Phuket.








Release site: Khao Phra Thaew non-hunting area (KPT)

Since 2002 GRP has been reintroducing breeding families of white handed gibbons (Hylobates lar) into the KPT forest. This forest was chosen since it is the largest remaining evergreen rainforest on the mainland of Phuket covering an area of 2,228 ha. This is large enough to sustain more than 60 gibbon territories, if accounting for average white-handed gibbon territory sizes of 24-30 ha. The white handed gibbon is native to Phuket, but the species was poached to extinction here between the 70’s and early 80’s. Because the forest has not been logged, or dramatically disturbed, since the wild gibbons disappeared we knew that the habitat could still support a healthy population.

Before the release of a gibbon family GRP will select a release site and prepare the new family’s territory by cutting a trail network of 50m x 50m squares at set coordinates. This trail network is essential in order to allow post release monitoring.

Gibbons are part of a healthy rainforest ecosystem and are believed to fill an important role as seed dispersers when they consume fruit and spread the seeds of many rainforest trees.

The Reintroduction Specialist Group with the International Union for the Conservation Of Nature (IUCN/SSC) states in their Guidelines that reintroductions should primarily take place in areas where a species has already become extinct and that one should avoid mixing reintroduced animals with wild counterparts. GRP is currently complying with international reintroduction guidelines in all essential aspects of our work, from the pre-release veterinary checks, the choice of release site to the extensive post-release monitoring of released animals.

Release method:

GRP uses a soft release reintroduction method which allows the animals to gradually gain independence from humansOnce a rescued gibbon has passed its Quarantine stage with medical examinations and graduated through its Rehabilitation – mainly reduced its dependency on human contact, established a pair bond with another gibbon, bred and raised at least one baby past infancy – the gibbon and its family is finally deemed ready for a return to the wild. The breeding family is an essential release criterion at GRP, and has long been interpreted as evidence of stable pair bonds in gibbons.

In the last stage of release preparations the family is moved further into the forest to spend 3-4months in a training or acclimatization cage, located within the territory that has been chosen for the family. On the release day the cage is opened and left open for a few days to allow the gibbons to go in and out while they get used to their new environment. By housing the gibbons within their new “territory” prior to release the animals are more likely to feel at home there and stay around the familiar site.


Supplemental feeding:

The gibbons will need supplemental feeding for a long time after release while they learn to forage for themselves. All feedings happen via a basket that is pulled up into the trees. After being fed twice a day during the first weeks in the wild, we reduce feeding times to once a day to encourage the family to start exploring more of their territory. Initially the family is fed the same amount as the captive ratio, at 1kg per day per individual, but as they learn to find wild foods we will gradually decrease the amounts until finally ceased. To help the family expand their territory the feeding station is moved further into the prepared territory with time.

Average time to independence (the time between release and the stopping of supplemental feeding) is around two years for the successfully reintroduced gibbons in KPT.

Follow up and post-release monitoring:

After the release the GRP will do 24 h/day post-release monitoring of the family for the first one or two weeks and subsequently the gibbons will be observed every day for one to two years. Much of this monitoring happens in conjunction with the daily feeding, but we also collect behavioural data on the released individuals as often as possible and for as many years as possible, when only the number of staff and volunteers available allows for it.
Behavioural observations are done every two minutes on a single focal animal per day, but will include social behaviours and distances between individuals in the group. We also monitor the gibbons’ height in the canopy and the area code where they are found every 10 minutes. Currently we mark down the gibbons’ locations on our GPS, but in the past satellite reception was easily lost under the forest canopy and we had to rely on our own trail network coordinates and handwritten maps.

We are able to monitor the successes of our reintroductions by physically following the gibbons and watching them. Due to the high costs involved GRP has not been using radio telemetry to follow released animals.

Observation 531209-Mon-ObHopeGr-1

KPT is a reintroduction site – Do not feed wild animals!

All released animals are forcefully discouraged from following or interacting with humans and observers are always keeping a distance of at least 5 meters from the animals. Sometimes it is impossible to accurately predict how an animal is going to behave once it is no longer caged; some gibbons may approach humans and their interesting smelling backpacks for food, whilst others may be aggressively defending their territory. GRP uses slingshots, containing harmless dried beans, to scare off gibbons that are giving people a lot of attention or spending time on the ground. However, GRP can not take responsibility for the behaviour of released animals.

Most gibbons will not approach humans, but some reintroduced ex-pet gibbons carry memories of unknown traumas and experiences from their past lives with humans and have little respect and fear of tourists that may try to feed them or interact with them in the forest.

Throughout the KPT forest GRP has put up signs to remind people that the forest is used as a gibbon reintroduction and research area and that under no condition should humans try to interact or feed gibbons that they see in the wild. Aggression towards humans may include the following behaviors: jaw-snapping, loud vocalization, vigorous locomotion, legs and arms spread (to show a large surface and consequently to increase the body size), touching, grabbing, and biting.