Australasian Science: Australia's authority on science since 1938

Climate Change KO’s Koalas

By Stephen Luntz

Koala numbers are falling, and the problem is likely to get worse according to evidence presented to a Senate inquiry into the health of the koala population.

Koala populations have crashed in many parts of the country. Queensland’s Koala Coast is increasingly misnamed, with populations falling by 51% in 3 years. In the region around Charleville, koala numbers have fallen from 50–60,000 in 1996 to 10–12,000 in 2009.

A/Prof Clive McAlpine of the University of Queensland’s School of Geography, Planning and Environmental Management says much of this fall has been caused by drought, and a rebound may be occurring after the recent rains. Nevertheless, he expects this to be a temporary reprieve as modelling by PhD student Christine Adams-Hosking predicts that koala habitat will increasingly contract towards coastal areas.

“Under a future hotter and drier climate, current koala distributions will likely shift to eastern and southern regions, where koala populations are already under threat due to high human population densities and ongoing pressures from habitat loss, dog attacks and vehicle collisions,” Adams-Hosking says.

Koala numbers are growing in Victoria and on Kangaroo Island, sometimes to the point of overpopulation. However, McAlpine says the genetic diversity in these areas is very low after the populations were almost wiped out by hunting.

“Chlamydia has been around for a while and is a problem mainly for the urban and peri-urban populations who are under stress from land use issues,” McAlpine says. Now a new disease threat has emerged in the form of a retrovirus that may cause cancer in some populations. Initially restricted to northern latitudes, the retrovirus has reached Kangaroo Island, possibly via mosquitoes. In the space of 5 years the retrovirus has infected 36% of koalas there.

One ray of hope comes in the form of University of Sydney research showing that heavy tree planting around Gunnedah in the 1990s has led to a boom in koala numbers in the area.

“Unfortunately,” says Dr Mathew Crowther of the School of Biological Sciences, “koalas will use trees planted next to roads, train tracks and fence lines. We saw very high rates of koala mortality in these areas. We also saw signs the small patches of trees available to koalas could not support them during tough times, such as droughts, when resources are scarce.”