How much can a koala bear?

By Rachel Sullivan 25 June 2009
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Is this beloved national icon a threatened species, or a plague? It all depends where you look.

There are less than 100,000 koalas left in the wild throughout mainland Australia according to the Australian Koala Foundation (AKF).

To blame, it says, are habitat destruction and fragmentation, drought, cars, domestic-dog attacks, bushfires and a lack of Federal Government legislation – in Queensland, koalas are listed as both ‘common’ and ‘vulnerable’; in NSW, they’re ‘vulnerable’; in Victoria they have no official listing; and in SA they’re ‘rare’.

The government considers the protection of the species to be primarily each State’s responsibility. The States, in turn, largely pass on responsibility to local government, which often has the least resources and expertise in wildlife management or habitat assessment.

But according to the AKF’s Victorian liaison officer, Rolf Schlagloth, the problem began in the early 1900s, when more than 3 million koalas were killed for their fur. “Populations were so seriously depleted in some areas that they’ve never recovered,” he says. “At the same time, as much as 80 per cent of the animals’ natural forest habitat was destroyed when it was converted into farmland.”

Well-meaning people sought to protect koalas by taking a few to islands where there were no predators and little competition for resources. Without the usual regulatory mechanisms, koala populations exploded, leading to inbreeding – most notably on Kangaroo Island, where the population estimate is 27,000.

According to Glenn Shimmin, senior ecologist with the SA Department of Environment and Heritage, the problem with having too many koalas is twofold.   They become malformed through inbreeding and they kill their food trees by stripping them of foliage. “All of the other animals that depend on those trees also suffer,” Glenn says.

Rather than culling them, Glenn’s been sterilising island populations and translocating thousands of koalas to the mainland. “Unfortunately, these koalas can’t always territorialise successfully, and mortality rates can be high,” he says.

But habitat loss remains the leading cause of declining mainland populations. Alistair Melzer, a senior research fellow at Central Queensland University’s Centre for Environmental Management, has spent the past 20 years working on koala populations in south-east Queensland. “Even in the best conditions, the drought has led to habitat changes,” he says. “At worst, widespread tree death has led to dramatically declining populations, and even the complete disappearance from parts of the range where once there were good populations.”

Source: Australian Geographic Jul – Sep 2008