A leading forest-communities advocate has cautioned that the new link between koala deaths and a 27-degree Celsius heat threshold risks confusing correlation with causation, pointing to the spring breeding season as an overlooked explanation for the surge in admissions. That is according to Steve Dobbyns, executive officer of Forest and Wood Communities Australia, in comments to Wood Central on the study of 11,862 koala rescue records across New South Wales.
The study, released this week, matched each admission to local weather records spanning 2000 to 2022 and found the odds of a koala being admitted or dying increased by 1.5 to 3.5 times once seven-day temperatures exceeded 30 °C. Its lead author, University of Sydney behavioural ecologist Valentina Mella, has called the work the most comprehensive link yet drawn between rising temperatures and koala mortality.
Dobbyns welcomed the research as a worthwhile contribution but said a statistical association of that kind could not, on its own, establish what was killing the animals. “Correlation doesn’t necessarily prove causation,” he said.
His central objection turns on timing, because the spring and summer breeding season coincides with the hot, dry months singled out by the study as most dangerous. Koalas cover far greater distances in that window as they search for mates and territory, he said, which leaves open the possibility that heat marks the calendar rather than the cause.
That heightened movement carries its own toll, with roaming animals running into cars, dogs and other hazards far more often than settled koalas. The breeding surge, he said, “coincides with hotter months and drought conditions,” so higher temperatures “may simply overlap with periods of elevated movement and stress rather than being the sole driver of mortality.”
A second caution concerns the data itself: rescue admissions count only the koalas people find and deliver into care, rather than total deaths across the landscape. Dobbyns said animals moving more often near roads, towns and farms were “more likely to be detected and admitted to care,” which could overstate the apparent toll in settled districts.
He was careful not to play down the heat risk, acknowledging that hot weather and drought clearly affect koala health and survival. Pinning rising deaths on a single number, he said, oversimplifies a picture that involves “a much more complex interaction between breeding behaviour, seasonal movement, habitat condition, disease, predation and human interaction.”
For Dobbyns, the threshold makes a compelling headline but will carry weight once researchers can separate heat from the breeding-season movement that peaks across the very same weeks — a distinction he says the current admissions data cannot draw on its own.
