Measuring the success of wildlife rehabilitation: Koalas and Brushtail possums

Native mammal populations in Southeast Queensland are under threat from habitat loss through land development, dog attacks and motor vehicle accidents. Animals that are not killed from these impacts are sometimes rescued, rehabilitated and later released back into the wild, usually in their area of origin. Although the release of these animals is a relatively common practice, little post release monitoring has been carried out and reported to assess the success of the animals in the wild. This paper discusses the results of three recent studies which have monitored the movements and health of rehabilitated and translocated koalas (Phascolarctos ciniereus) and common brushtail possums (Trichosurus vulpecular): one conducted by Wildcare Australia in 1995- 1996, the other two in collaboration with the University of Queensland. The results indicate that the survival and health of the great majority of the released animals were good and that they were usually able to establish new home ranges during the tracking period. Such findings seem to contradict the results of studies conducted in southern Australia which have monitored the release of translocated possums and gliders, and suggest that there are some key factors which may be critical in determining the success of such releases. These factors include the age of admission and the duration of care, and in particular the selection of the release site. With both koalas and brushtail possums, the release site was found to be critical in determining both the survival and dispersal of the released animals. Consequently, while these studies confirm that the reintroduction of koalas and common brushtail possums may be a viable management strategy, the individual characteristics of the animals themselves and of their release areas must be carefully considered. It is recommended that further research of these key release factors be undertaken and that the work be extended for other species which are commonly released following rehabilitation.