Every night, tens of thousands of grey-headed flying foxes fan the skies over Melbourne, Australia.
During the day, these large bats congregate in the trees they help pollinate, dangling from branches as they nap or chatter to each other. At night, they flit across the state of Victoria in search of food: leaves, flowers, and fruit.
But a summer danger threatens their mostly peaceful existence. When the temperature rises above 104 degrees Fahrenheit, thousands die at once.
Such sultry days are becoming more and more common. The eight years between 2013 and 2020 were among the 10 warmest on record in Australia. So officials in Melbourne, a city once known as Batmaniahave come up with a solution: They give the bats a shower.
This year, for approximately $120,000, 32 custom sprinklers were installed along the river in Yarra Bend ParkMelbourne’s largest natural bushland park and the site of the bat colony, which numbers around 35,000 in summer.
The system, believed to be the largest and most advanced of its kind, should lower temperatures in a given area by about 10 degrees Fahrenheit, said Brendan Sullivan, Parks Victoria’s chief ranger.
Designing it was fraught with complications, he said. Aside from the usual noise, durability and logistics concerns, the system needed to be protected from local cockatoos, who tend to pull things apart with their beaks.
Technicians struggled to replicate a light rain shower, which would cool the bats, without raising the humidity too much, which threatened to do the opposite. The resulting structure, which uses filtered river water, resembles a series of towering metal cattails.
But would the bats use it?
“They’re much smarter than we think,” Mr. Sullivan said. During trials, a lone bat made an unexpected test flight through the curtain of water before returning to the colony, chirping away, he said. Seemingly at the suggestion of the first bat, another bat followed, then another, and another.
“Eventually a whole bunch of bats arrived and just flew through,” Mr Sullivan said. “It’s like they were talking to each other and saying, ‘Come and look at this.'”
Flying foxes are known to work together, said Rodney van der Ree, an ecologist at the University of Melbourne. “They’re very smart,” he said. “A large number turn up in a new area when a large amount of food is available, so somehow they talk to each other.”
In December 2019, during the scorching months known as Black Summer, around 4,500 grey-headed flying foxes in Melbourne perished over three days of extreme heat.
On the hottest days, the strategies the bats normally use to deal with hot weather, such as panting or flapping their wings, no longer work. As dehydration sets in, mental function declines and some animals experience seizures. In the end, they die without urgent care.
Volunteers describe the trauma of seeing life emerge from the animals’ fox-like faces and knee-deep into the carcasses of creatures they had rescued for years.
“You despair for a while, but you have to pick yourself up and carry on because that’s the only response you can get,” says Lawrence Pope, 62, who has worked with Melbourne’s bats for about two decades. He added, “If they don’t have you to help them, they don’t have anyone.”
In flight, the bats carved a gothic figure, with wings swinging three feet long. They hang head down in the trees and resemble old boots. Up close they have the appearance of a mammal with large eyes, a rusty collar of chestnut fur and large, curious ears. (They don’t echolocate.) Baby bats often hiccup.
“They seem to be really sweet,” says Sarah Frith, a veterinarian at Zoos Victoria who has treated sick flying foxes. “Not aggressive, very gentle and just a pleasure to be around.”
But among many Australians, the animals get a bad reputation for being smelly, noisy and, possible disease vectors. For ecologists, their dwindling numbers, about 700,000 in 2019 compared to many millions before colonization, are disturbing. The bats are a “keystone” species and play a vital role in the pollination of many native trees.
Mr. Pope, along with his wife Megan Davidson, rescue orphaned bats – this year Stinky, Manky, Hanky, Panky and Wriggle – and raise them in wicker baskets until they are old enough to return to the colony.
On a recent Sunday, in a makeshift structure used as a shelter for pubescent bats, he climbed a stepladder to fill a water bucket hung on the wall for the bats to use. Stealthily a bat reached out from its roost on the ceiling and snatched away his sun hat.
Flying foxes face multiple risks in the city, including barbed wire, tree nets and electrocution from power lines, Mr Pope said. He was optimistic that the sprinklers would save “quite a few of them” from extreme heat, he said.
Although grey-headed flying foxes are native to Australia, they have been transplanted to Melbourne, forced further south by habitat destruction a few decades ago.
When the bats first appeared in Melbourne’s lush botanic gardens in the 1990s, they were a novelty, said Simon Toop, a project manager at the time in the Department of Sustainability and Environment.
But as their numbers increased and their presence began to annoy visitors, they came to be considered pests, he said.
“It got to the point where the animals were actually shot in the gardens to try and mitigate the impact, and that’s when the government stepped in,” said Mr Toop.
Killing the bats, a protected vulnerable species, was unsustainable – especially when animal rights activists, including Mr Pope, started camping under the trees. And so the local government launched an ambitious, sometimes farcical campaign to drive the bats out of the botanic gardens, where they had become accustomed to succulent, year-round foliage.
The team, led by Mr. Toop, harassed the bats by making banging noises the animals disliked, such as the whizzing of a street sweeper, and flashing lights at them. In some cases, people hissed or banged on the lids of garbage cans, Mr. Toop said.
After two weeks of unrest, the bats decided to leave the Botanical Gardens. Over the next eight months, they migrated from one prime real estate location to another: ornamental gardens, a private girls’ school, the backyards of wealthy Melburnians.
Wherever they went, Mr. Toop’s team always showed up. Finally, he said, the flying foxes came to recognize them.
“They would see me, shout and make noise,” said Mr. Toop. “If other people came in, they weren’t too concerned.”
Eventually, the bats moved to their current location, along the river from where authorities had hoped to relocate them. Since the females were due to give birth soon, this seemed like an appropriate compromise, Mr. Toop said, and local officials worked to improve the site to meet the animals’ needs.
Two decades later, sprinklers are the latest attempt to make bats comfortable. But the water is only turned on when there is a real risk – especially with more and more extremely hot days.
In a warming world, bats will have to adapt to a warmer climate, says ecologist Dr Van der Ree. “Stress is important from an evolutionary perspective,” he said. “We would prefer that the bats that can handle the heat pass on their genes, even more than the bats that can’t.”