1997: Tower Hill Game Reserve. Subdermal implants applied to female koalas for contraception

Hunted, marooned, re-introduced, contracepted: a history of Koala management in Victoria

Peter Menkhorst

“…At a meeting of the Australian and New Zealand Environment and Conservation Council (a forum of State, Commonwealth and New Zealand Environment Ministers) held in May 1996, culling was rejected as a management tool. Consequently, it was not considered during preparation of the National Koala Conservation Strategy published in 1998 (ANZECC 1998).

Counter balancing concerns for individual animal welfare is the increasing concern amongst land managers and conservationists about the ecological damage resulting from Koala over-browsing (Koala Management Task Force 1996; ANZECC 1998; Masters et al. 2004; Menkhorst 2004).The search for an alternative to translocation began in earnest in 1995 when the Department of Natural Resources and Environment commissioned a review of fertility control options (Middleton 1996a). The outcome of the review was a recommendation to conduct separate field trials of the effectiveness of two techniques – slow-release implants of a progestin hormone or oestradiol to females, and vasectomy of males (Middleton 1996b). Implementation began in late 1996, despite opposition from some quarters because it was feared that the program would divert money away from other urgent wildlife research and management programs, and because of doubt about the efficacy of male sterilisation (eg. Anderson 1996). So began a decade of intensive research and adaptive management trials by the Victorian and South Australian wildlife management agencies to develop methods for in-situ population control (Table 2).In Victoria, these trials have been guided by an expert advisory committee, the Koala Technical Advisory Committee, convened jointly by the two Government agencies with primary responsibility for Koala management, the Department of Sustainability and Environment and Parks Victoria. The committee’s role is to advise the two Government agencies on technical matters relating to Koala management. Its primary focus in recent years has been to advise on adaptive-management trials to assess a range of fertility control techniques for their efficacy, ethics and cost-effectiveness. 

“A six-year field trial of subdermal implants containing either the synthetic progestin levonorgestrel, or low doses of oestradiol, applied to female Koalas, began at Tower Hill Game Reserve in 1997. This trial indicated that a contraceptive rate of 100% could be maintained for up to six years using levonorgestrel implants, representing at least 60% of the reproductive life of a female Koala (Middleton et al. 2003; DSE unpublished data). A trial of the impact of vasectomy of male Koalas was also conducted at Red Bill Creek on French Island between November 1996 and October 1998. By vasectomising all males captured on the study site (the proportion of treated males on site varied over time because the population was not a closed one) this program reduced the proportion of females carrying pouch young from 87% at the beginning of treatments to 36% over two breeding seasons (DSE unpublished data).”