Koala encounters

The Koalas of Far North Queensland could hold secrets to the species’ survival.

For a moment, spotlights cease bouncing off leaves and branches of Gum-topped Box (Eucalyptus moluccana). Conversation clusters around a thermal drone controller at Yourka Reserve, four hours south-west of Cairns in Queensland on Jirrbal and Warrungu Country. 

A question erupts: “Is that one?”

Anticipation builds as a white-hot mass on the screen is investigated.

“Close. But it’s just a termite mound that’s still holding heat from the sun,” confirms pilot Richard Hopkinson. For two nights researchers and Bush Heritage staff have searched for Koalas (Phascolarctos cinereus).

Since colonisation began, Koala numbers have experienced widespread decline, mirroring the loss and fragmentation of available habitat. Now, in Queensland, New South Wales and the Australian Capital Territory, they are listed as ‘endangered’ under the Environment Protection and Biodiversity Conservation Act 1999. 

Roger Martin, a wildlife biologist, is part of the group and has studied the animal since the seventies. 

Roger and Richard are also accompanied by wildlife vet Dr Amy Shima. Together, they’ve been leading studies on the northern population for more than four years. Far less research has been conducted on the Koalas of the tropics – and they’re quite different characters altogether. They’re smaller, with shorter, thinner fur to cope with humidity and heat, and they’re also much paler. 

“These Koalas are almost white on their rear and belly, which could be to do with high solar radiation, or part of their repertoire of cryptic behaviours,” says Roger. Their colour makes them tricky to spot in a forest where the trunks of their favourite trees – E. moluccana, Corymbia citriodora or E. tereticornis – are mostly pale coloured. Harder still, given they’re a low abundance population.

The Atherton Tablelands mark the tip of their range, with fewer than 40 reported sightings in the past 20 years. “There are probably a few thousand animals scattered across thousands of square kilometers,” says Roger. But it’s this population that could hold the keys to the species’ survival.

Roger and the team’s research show these Koalas move lengthy distances, up to 3 km a night during breeding season, and have extensive home ranges, sometimes up to a thousand hectares, suggesting they’re well adapted to their hotter, drier and scarce predicament.

Also part of the group is Christine Mauger, ecologist for Bush Heritage. 

Since 2007, when supporters enabled Bush Heritage to protect the reserve, dedicated on-ground management of weeds, invasive species and fire has allowed biodiversity at Yourka to flourish. 

“The homestead sits at about 650 metres above sea level. As you move further east into the rockier areas, this increases to 950 metres. So, there’s a lot of variety in different landscapes, temperature and rainfall,” says Christine.

Across 43,757 hectares, the reserve is home to 29 regional ecosystems and offers a large swathe of prime remnant habitat for Koalas and many other native animals. 

“We want to complete intensive studies on them [Koalas] to see what their behaviours are, which parts of the reserve they’re using, whether they’re interacting with other Koalas, their health status, and their favourite feeding and habitat trees,” says Christine.

To do this, the team returned to the creek line where Koalas were found in 2024. Over two nights, their method integrated thermal drone, traditional spotlighting and acoustic recording, which had already begun to pick up early breeding-season bellows from males.

“It’s a very low frequency call. Koala sound goes down to about 15 hertz, we [humans] can hear down to about 20 hertz. So, a lot of what’s going on is outside our hearing range,” says Roger.

Roger and Amy are using AI to search their recordings to recognise specific mating calls and better understand breeding behaviour. “One of the main challenges for a low abundance population is finding someone to mate with,” says Roger.

In the south, the opposite is often true, with populations in South Australia and Victoria considered stable or, in some cases, overabundant. Koala’s unequal response to environmental change across their range has made management complex.

A study completed last year by The University of Sydney looked at the entire Koala genome – more than 26,000 genes – and found inbreeding occurring throughout Victoria and South Australia and even as far north as Brisbane. High-density living in the south is decreasing genetic diversity. 

“It’s likely because populations are living in habitat which has been subdivided into small blocks, so they can’t move over large areas,” says Roger. “The males are mating with closely related females.”

Conversely, the study showed the northern population is more heterozygous – there is greater diversity in the genome – making them more resilient to change in climate and habitat, and probably more resistant to disease so they’re likely to have higher reproductive success. 

As temperatures rise, other threats to the species intensify. Understanding the heat-adapted and diverse population at Yourka is critically important for the future of the species and its habitat.

At midnight, after surveying over 60 hectares, the team retired. Their logbooks note Northern Greater Gliders (Petauroides minor), many macropods and Brushtail Possums (Trichosurus vulpecula), but no Koalas – only fresh claw marks on pale gums.

“Part of the reason for me, an aging biologist, returning to work on Koalas is because it’s such a valuable species to get the message across of just how necessary the conservation of broad tracts of habitat is,” says Roger •