The $358,000 plan to implant contraceptives in up to 2,000 koalas will take place over the next 10 weeks at a national park in the west of Victoria state, said John Thwaites, the state's environment minister.
"It would serve no one's interests if Victoria's koala management strategy wasn't about conservation of the species, and this means controlling population numbers where the animals are eating out their own food source and protecting natural habitat where numbers are low," Thwaites said Thursday.
Koala populations are unevenly spread across the state, Thwaites said. In some areas population density is so high that local vegetation is being destroyed.
Trials of the slow-release hormone show that it prevents conception for up to six years, he said.
While koalas in Victoria are thriving, they are in danger of extinction in much of Australia's eastern seaboard, conservationists warn. They say urban sprawl is destroying the koalas' habitat. They survive on leaves from a small number of eucalyptus tree species.
Meanwhile, on Kangaroo Island, off Australia's south coast, some environmentalists have urged authorities to shoot hundreds of koalas because the animals are destroying the island's vegetation. Authorities have rejected the call, concerned about a possible backlash among international tourists.