The heat. Obviously the heat. That's the first reason at least 700 flying foxes dropped dead from trees in the NSW upper Hunter Valley town of Singleton over the weekend, as temperatures hit 47 degrees on both Saturday and Sunday after a 45.5 degree Friday.
The Singleton deaths depicted in the sad video below were in addition to countless flying fox deaths over the weekend elsewhere across NSW, QLD and South Australia.
But why? Why can these animals not seek a source of water or do something to stop themselves succumbing to extreme heat?
The Huffington Post Australia put that question to Jaala Presland, whose husband shot the video above. In her day job, Jaala works in finance in the community services sector (although she's currently on maternity leave). She's also the bat* co-ordinator at Wildlife Aid in Singleton.
"It's a question we asked ourselves," Presland said. "Why just hang there and die? Because the natural instinct is to stay within the colony. The second they leave the colony they're open to predation.
"When it gets very, very hot, I've seen some fly out on their own and risk it, but they're often too far gone at that stage and don't make it to the river."
So tragically, most bats just hang until they literally expire.
But there's another reason behind the mass deaths in Singleton, which may be playing out in other towns too. In a word, shade. Or rather, the lack of it.
"This colony is smack in the middle of Singleton and they have very little shade," Presland said. "The trees they have are gum trees and Norfolk Island pines, but it's basically just a few small trees."
Larger trees which offered more shade for bats were moved from the centre of Singleton a few years ago for OH&S reasons. In other towns, trees have in the past been cleared illegally to get rid of bat colonies, because some residents consider bats pests.
This particular case of bat vs human in Singleton involved no maliciousness on the human side. It was just a case of weather too hot, shade not sufficient.
There were similar scenes elsewhere. At least 2000 bats died further north in NSW over the weekend, while bats have also died in Qld and South Australia in recent weeks.
And these events are becoming more common. Presland estimates that as many as 2500 bats died in 2004, when the town had two straight days of 45 degrees. Meanwhile the RSPCA said as many as 100,000 bats may have died in a Queensland heatwave in 2014.
So what now for the Singleton bats that survived?
Presland said another colony may move in. But any mass bat deaths are a worry. The majority of dead bats in Singleton this week were grey-headed flying foxes, which are listed as vulnerable. The greys are Australia's largest bat with an adult wingspan of a metre. And guess what? No two are the same.
"They're a really interesting little species and they definitely have personalities," Presland said. "You you get to know a bat's personality, especially when you raise orphaned babies."
*We've used the words "bat" and "flying fox" interchangeably in this story.