31 Mar 2021


WWF-Australia’s Threatened Species and Climate Adaptation Ecologist Dr Kita Ashman has a soft spot for flying foxes. Here she explains why, and how a simple strategy might provide just the cool change they need.

Australia's summers are getting hotter; that's for certain. As the recent catastrophic bushfires demonstrated, our unique ecosystems, plants and animals are under threat like never before.

And it's not only charismatic creatures that are at risk. A myriad of other important but lesser-known species are also being pushed to their limits. Like one of my personal favourites, flying foxes.

When the mercury soars above 40 degrees, these dark, heavily furred animals are highly vulnerable to heat stress in their crowded camps, some of which are home to thousands of individuals. And as we've seen in recent years, Australia's summer heatwaves are proving deadly.

Flying foxes are nocturnal animals and rely on roost trees to rest during the hottest parts of the day. But when their bodies begin to absorb or produce more heat than they can release, their internal temperatures soar. 

Flying foxes
Flying foxes © Geoff Brooks via Unsplash

At first, the flying foxes try to cope by fanning their wings and licking their wrists and wing membranes. When that doesn't work, they become really stressed and start to pant, which only accelerates dehydration. Clumping together to compete for what shade is available only makes them hotter, and we often see flying foxes move lower and lower down their roost trees to seek the protection of vegetation. If the hot conditions persist, as happens during a heatwave, dehydration eventually causes organ failure. It's a slow and painful death.

During the past four years, the hottest summers on record in Australia have resulted in prolonged heatwaves, droughts and bushfires, and we've lost tens of thousands of flying foxes that’ve been unable to adjust fast enough to our rapidly changing climate. They've literally dropped dead from the trees.

Australians have something of a love-hate relationship with flying foxes. Home gardeners spurn them for raiding their fruit trees, and some regard their urban camps as noisy and smelly. Yet flying foxes are vital to keeping many of our ecosystems balanced and healthy. Travelling thousands of kilometres up and down the eastern seaboard on their annual migrations, they disperse seeds and pollinate native plants over vast distances. They are actually unsung heroes, not villains.

Without these hard-working, long-distance gardeners, many of our native forests and woodlands would simply not exist. And without these forests, a whole host of other precious Australian animals and plants, some of them already threatened, would disappear, too.

So as Australia grapples with some of the highest rates of species extinction in the world, it's not only the cute and cuddly animals we must protect in order to maintain biodiversity. At least one flying fox species - the grey-headed flying fox - is among our most vulnerable mammals.

The combined threats of climate change, habitat loss, invasive species and disease could easily bring about the extinction of flying fox species. It would be devastating, for the flying foxes and our native forests.

Atmospheric cooling system in action for grey headed flying foxes
© WWF-Australia

Which is why the successful Victorian trial of a cooling system for flying foxes has filled me with renewed hope.

Jointly funded by WWF-Australia, the City of Greater Bendigo, and the Department of Environment, Land, Water,and Planning, the system was installed in December 2020 in the tree canopy in Bendigo's Rosalind Park, which is home to an important breeding colony of grey-headed flying foxes. When the temperature and humidity reach certain levels, aerial sprinklers automatically switch on, giving the flying foxes and their surrounding vegetation a light shower.

Over three days from 23-25 January, when temperatures in the park climbed as high as 41 degrees, no flying fox deaths were recorded. Researchers from WSP Australia and staff from the City of Greater Bendigo found that the sprinklers kept the test zone 2 degrees cooler and saved the animals considerable heat stress.

I was fortunate enough to be there on a sweltering hot 40 degree day on 11 January when they tested out the sprinkler system for the first time. The flying foxes were a little startled at first but soon moved closer to the sprinklers, stretching out their wings to cool themselves, and licking the water droplets. I know I was jealous of the cooling spray. It was a far cry from the summer of 2020, when a record-breaking heatwave saw 220 die from heat stress in this same park - one of a series of mass flying fox mortality events in eastern Australia.

Sadly, many of the casualties during these events are young flying foxes (known as pups) and their lactating mothers, whose energy levels are already depleted due to nursing. Their deaths can be a huge blow to the recovery of populations because females only give birth to one pup each year.

Sprinkler system gives hope to flying foxes
© WWF-Australia

Around Australia, flying fox numbers have decreased dramatically over the past 50 years, due to habitat loss and changing climatic patterns. Heatwaves are set to become more common and severe as climate change intensifies. Flying foxes must contend not only with higher average daytime temperatures but also hotter nights when they would normally get some relief.

I'm encouraged by the results of the Bendigo sprinkler trial and thrilled that a simple measure may help prevent thousands of flying foxes from suffering and dying during Australia's increasingly hot summers. While the atmospheric cooling system needs a little more testing, it holds promise for other flying fox colonies and even other animals equally vulnerable to climate change.

Historic habitat loss has already put flying foxes in a perilous position. Human-induced climate change is now compounding their predicament. But as I saw in Bendigo in January, we have the power and the technology to make a positive difference in our changing world. It's that firm conviction that drives my species conservation work.

The health of our forests and, indeed, entire ecosystems depend on pollinator species like flying foxes. And flying foxes now depend on us. Like all native species, they don't have a voice, so we must be that voice for them.

You, too, can help protect Australia's biodiversity by joining our call for stronger action on climate change as WWF continues to work to regenerate nature by 2030.