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Data are presented from an island in Central Kalimantan, Indonesia which has …

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- Wildlife reintroduction: considerations of habitat quality at the release site

Tropical forests continue to disappear at a phenomenal rate and the illegal pet trade continues with no sign of abating any time soon. The numbers of gibbons being kept in captivity will only increase as their forest homes are opened up for plantations, logging concessions and for access. Rehabilitation can work in conjunction with habitat protection in terms of protecting areas for reintroduction and establishing rehabilitation training centres where there are already wild gibbons. Rehabilitation and reintroduction is becoming the only viable option to save the hundreds, possibly thousands of pet gibbons all over the world and to repopulate the large tracts of forest which no longer have gibbon populations due to hunting.

In the IUCN/SSC Reintroduction Specialist Group: Guidelines for Non-human Primate Reintroductions [21] it is stated "reintroductions should only take place when the taxon's habitat requirements are satisfied and likely to be sustainable for the foreseeable future. If the taxon's basic habitat and ecological requirements cannot be determined, the animals should not be released." The only way to meet these requirements is to conduct habitat analysis of the release site, both pre- and post-release. Here I have shown that the release island of Mintin has the capacity to support at least three groups with about 5 gibbons/group (15 individuals). Although extrapolations of gibbon food trees estimates the maximum population size to be 19 individuals, there is competition from other animals, which is likely to prevent Mintin supporting four gibbon groups. The accurate analysis of the release area is essential if the released animals are going to survive in the future and for them to become nutritionally independent as soon as possible post-release. I recognise that gibbons released onto an island will not be viable for establishing a long-term population as the island cannot sustain a large population indefinitely. Nevertheless, it is important that releases of animals are carried out in a manner that allows post-release data to be collected. Using the island as a half-way house for the released gibbons allows us to assess their adaptation and identify any problems. A half-way house is an area of good quality forest were reintroduced animals are released immediately following the rehabilitation period in the cage [22]. The half-way house allows the released animals to adapt to the forest while remaining under the care and supervision of project staff i.e. the animals will be monitored to observe how they are adapting to the forest. The half-way house is generally a small, isolated area of forest where the animals are free to roam but where they can still be located if there are any problems. Due to the lack of accurate and reliable data on the behaviour of released gibbons it is essential that all stages of the rehabilitation and release process are monitored. It is not known how gibbons will adapt to the forest without a half-way house experience, the purpose of the half-way house is to identify any problems quickly and to ensure all animals are adapting well to the wild. As long as there are limited data available on the behaviour of reintroduced gibbons, the slow approach using a half-way house is by far the sensible. Without information from the animals' behaviour in a half-way house setting, we risk releasing unprepared animals who will be difficult to follow and monitor. Using this study as a template, future releases can take place in contiguous forest. This is a preliminary study based on available data and one of the first of it's kind to attempt to address issues of habitat suitability at release sites. This study looked at the important aspect of the relationship seen between gibbon population density and floristic composition. I am aware that predator densities, the densities of other frugivore competitors, human impacts, demographic stochasticity in births/deaths are important aspects but are not variables ones that can be reasonably studied for an initial assessment of a release area. These variables should form the basis of the long-term post-release monitoring of the release site and the impact of the gibbons on the island.

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