A stand of pine trees near the Adelaide zoo erupts every sunset as tens of thousands of megabats take to the sky. The metre-wide, scalloped wings of these grey-headed flying foxes silhouette against the sky like the summoning sign for a certain superhero.
Flying foxes first appeared in numbers in Adelaide around 2010 after climate change-related food shortages drove them further south. Drought conditions and habitat loss forced them out of New South Wales and Victoria, and once they found a good spot they settled in – and bred.
Nowadays they gather in a single, enormous colony in Botanic park – about 46,000 of them – before heading out for a night’s feed, causing disruption along the way.
“For an urban camp [those numbers are] pretty high … it’s up there with the highest we’ve had in South Australia,” says Jason van Weenen, Green Adelaide’s urban biodiversity team leader.
“2010 was the first year we had a colony arrive; that was associated with the species having some real trouble in the bulk of their eastern range.
“Those tough conditions resulted in them finding Adelaide and now they’ve incorporated it into their foraging.”
The grey-headed flying-fox (Pteropus poliocephalus) is native to Australia and is one of the world’s largest bats. Sometimes referred to as fruit bats, they weigh around 700g and they do not use echolocation – unlike microbats, which and can weigh as little as three or four grams.
A newer, smaller SA colony has set up near the regional town of Millicent, and it is expected that other camps will be established. But temperatures of around 38C can be fatal for the megabats, especially the pups – a major issue in recent years.
In Adelaide, a sprinkler has been hoisted up to tree level to try to cool them down, and they can occasionally be seen drinking or even swimming in rivers.
This year’s mild summer and good resources have seen the colony’s numbers surge, with successful breeding and no significant heat stress events.
By day they bunch in trees like rustling garbage bags with their fluffy, fox-like heads poking out. By night they seek eucalyptus tree nectar as well as fruits, including figs, apples and pears.
But while on their hunt, they can cause damage. The young tire more easily and find resting spots along power lines, leading to power outages.
Paul Roberts, head of corporate affairs at SA Power Networks, says February and early March are the “worst times for bat-related outages” as the new brood spreads its wings.
“Customers can experience either extended outages when an animal gets caught on powerlines, or short ‘momentary’ outages, as equipment reconnects power if the animal falls clear after contacting overhead powerlines,” he says.
“Most of these outages occur in the early hours of the morning when the young tire while foraging for food and try to land on electricity poles tops for a rest.”
In 2023, there were plenty of momentary outages as well as 55 sustained outages, with power lost to 72,000 customers. Roberts says they are expecting more outages this year, though “thankfully” mostly in the early hours.
SA Power Networks is working on fixes. Animal guards – Frisbee-like plastic devices – are being attached where powerlines are the most affected, but the bats’ flight paths are random, making it hard to be systematic. So crews put the guards on as they’re working on other issues, or if they have spare time.
“We will do everything we can to minimise the impact, but given the colonies are growing and we have hundreds of thousands of poles, we have a lot of work to do over the next decade installing animal guards and covering more of our powerlines to be able to significantly reduce what tend to be randomly located bat-related outages,” Roberts says.
Bats can carry lyssavirus, although human infection is rare. They can also carry Hendra virus, which can infect horses and from there be passed on to humans, but horse vaccinations have diminished that risk.
“It’s been a steep learning curve,” Van Weenen says, because the population is both protected and a “challenge” to infrastructure and industry.
“Every species has its own quirks and characteristics and the flying foxes are very different to other species here in SA.
“If you get scratched or bitten, go and get your rabies shot,” Van Weenen says. “For us in SA, the colony’s fairly new, so we’re just reminding people that it’s important not to touch them – trained professionals are vaccinated and can handle the bats safely and look after them.”
In back yards all over metropolitan Adelaide, grey-headed flying foxes can now be heard squawking and squabbling over the choicest food – they’re fond of river red gum and blue gum nectar, and go bananas for lemon-scented or spotted gums.
As dawn breaks, the colony heads back to its city camp to spend another day clinging to trees with their toes, furry heads poking out of their rustling, black wings.
