The 30,000 gray-headed flying foxes in Yarra Bend Park, just outside the heart of Melbourne, Australia, were having a fairly normal early spring.

In September and October—springtime in Australia and prime birthing season for the 11-inch long megabats—many of the flying foxes had returned to the park from their winter migration up the coast. Females were birthing pups as normal, says biologist Stephen Brend, who is in charge of monitoring gray-headed flying foxes in Victoria province, including at Yarra Bend Park, which is home to a significant colony of the bats. All was routine.

“And then the horror started,” Brend says. “It got too hot, too quickly.”

Incapable of surviving the extreme, relentless heat that gripped Melbourne in December, the flying foxes were