Every evening, tens of thousands of gray-headed flying foxes fan across the sky above Melbourne, Australia.

By day, these large bats cluster in the trees they help to pollinate, dangling from branches as they snooze or chatter to one another. By night, they flit about the state of Victoria seeking food: leaves, flowers and fruit.

But a summertime danger threatens their mostly peaceful existence. When temperatures rise above 104 degrees Fahrenheit, thousands die at once.

Such sweltering days are becoming 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 Batmania, have devised a solution: They’re giving the bats a shower.

This year, at a cost of around $120,000, 32 custom sprinklers were installed along the river in Yarra Bend Park, Melbourne’s largest natural bushland park and the location of the bats’ colony, which is about 35,000 strong in summertime.

The system, thought to be the largest and most sophisticated of its kind, should reduce temperatures in a given area by around 10 degrees Fahrenheit, said Brendan Sullivan, the chief ranger for Parks Victoria.

Designing it was fraught with complication, he said. Apart from the usual concerns of noise, durability and logistics, the system needed to be protected against local cockatoos, who tend to pull things apart with their beaks.

Technicians struggled to mimic a light rain shower, which would cool the bats, without overly increasing humidity, which risked doing 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 more clever than we give them credit for,” Mr. Sullivan said. During trials, a lone bat had taken an unexpected test flight through the curtain of water before returning to the colony, chirruping away, he said. Seemingly on the first bat’s suggestion, another bat followed suit, then another and another.

“In the end, we had a whole heap of bats coming up and just flying through it,” Mr. Sullivan said. “It’s like they were talking to each other, going, ‘Come and have a look at this.’”

Flying foxes are known to cooperate, said Rodney van der Ree, an ecologist at the University of Melbourne. “They’re very smart,” he said. “A large number will turn up in a new area when there’s a large amount of food available, so somehow they talk to each other.”

In December 2019, during the scorching months known as Black Summer, about 4,500 gray-headed flying foxes in Melbourne perished over three days of extreme heat.

On the hottest days, strategies the bats normally use to cope with warm weather, like panting or fanning their wings, no longer work. As dehydration sets in, mental function ebbs, and some of the animals experience seizures. Eventually, without urgent care, they die.

Volunteers describe the trauma of seeing life recede from the animals’ foxy faces, and of being knee-deep in the carcasses of creatures they had worked for years to save.

“You despair for a while, but you’ve got to pick yourself up and crack on, because that’s the only response to have,” said Lawrence Pope, 62, who has worked with Melbourne’s bats for around two decades. He added: “If they haven’t got you helping them, they’ve got no one.”

In flight, the bats cut a gothic figure, with swooping wings that span three feet. Hanging head-down in the trees, they resemble old boots. Close up, they have a big-eyed mammalian mien, a rusty collar of chestnut fur and large, inquisitive ears. (They do not echolocate.) Baby bats often suffer from the hiccups.

“They do seem to be really very lovely,” said Sarah Frith, a veterinarian at Zoos Victoria who has treated ailing flying foxes. “Not aggressive, very gentle-natured and just a real joy to interact with.”

But among many Australians, the animals get a bad rap as smelly, noisy and, potentially, disease vectors. To ecologists, their diminishing numbers, about 700,000 in 2019 compared with many millions before colonization, are distressing. The bats are a “keystone” species, playing a critical role in the pollination of many native trees.

Mr. Pope, along with his wife, Megan Davidson, rescues orphaned bats — this year, Stinky, Manky, Hanky, Panky and Wriggle — and raises 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 halfway house for adolescent bats, he climbed a stepladder to fill a water bucket hanging on the wall for the bats. Stealthily, from its roost on the ceiling, one bat reached out and purloined his sun hat.

Flying foxes face multiple risks in the city, including barbed wire, tree netting and electrocution from power lines, Mr. Pope said. He was optimistic that the sprinklers would save “a goodly number of them” from extreme heat, he said.

Although gray-headed flying foxes are native to Australia, they are transplants to Melbourne, forced farther south a few decades ago by habitat destruction.

When the bats first appeared in Melbourne’s lush Botanic Gardens in the 1990s, they were a novelty, said Simon Toop, then a project manager with the Department of Sustainability and Environment.

But as their numbers swelled and their presence started to irk visitors, they became thought of as pests, he said.

“It got to the point where the animals were actually being shot in the gardens to try and reduce the impact, and that’s when government stepped in,” Mr. Toop said.

Killing the bats, a protected vulnerable species, was untenable — especially when animal rights activists, including Mr. Pope, began to camp under the trees. And so the local government ran an ambitious, sometimes farcical campaign to expel the bats from the Botanic Gardens, where they had grown accustomed to succulent, year-round foliage.

The team, led by Mr. Toop, bothered the bats by blasting sounds the animals disliked, like the whoosh of a street cleaner, and flashing lights at them. In some cases, people hissed or banged on the lids of trash cans, Mr. Toop said.

After two weeks of disturbance, the bats decided to leave the Botanic 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 well-to-do Melburnians.

Wherever they went, Mr. Toop’s team would show up. Eventually, he said, the flying foxes came to recognize them.

“They would see me, scream and make noise,” Mr. Toop said. “If other people walked in, they weren’t too concerned.”

Finally, the bats moved to their present site, along the river from where the authorities had hoped to resituate them. With the females soon to give birth, this seemed an adequate compromise, Mr. Toop said, and local officials worked on improving the location to fit the animals’ needs.

Two decades on, the sprinklers are the latest effort to make the bats comfortable. But the water will be switched on only when there is a genuine risk — especially with more and more extremely hot days.

In a warming world, the bats will need to adapt to a hotter climate, said Dr. Van de Ree, the ecologist. “Stress is important from a evolutionary perspective,” he said. “Ideally, we want the bats that can handle the heat to pass on their genes, more so than the bats that can’t.”

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