The colony, which can range anywhere from 4000 to 70,000 bats depending on the season, fly out from their roosts in Yarra Bend Park in search of food.

It's a quest vital not only to their survival but also for the regeneration of Australia's forests.

"They're the bees of the night," says Fly By Night shelter owner Tamsyn Hogarth.

"They're after the nectar and blossom of our eucalypts.They're our only long-distance pollinator so if we lose them, we lose koalas."

Ms Hogarth runs her shelter from the Dandenong Ranges, with the small group of volunteers working to rescue injured animals and raise abandoned pups.

Hundreds of flying foxes end up in their care each year, mostly after being caught in tree netting, barbed wire and power lines.

"We could do one or two rescues each day," Ms Hogarth says.

"If the gums aren't flowering, often the animals will go to substitute foods like nectarines or other things in people's backyards and then they come into care.

"One year, I think we had 500 rescues in one month."

New Victorian regulations on tree netting were introduced in late 2021, with residents required to use 5mm by 5mm mesh or smaller.

But Ms Hogarth says not enough people are aware of the changes and the flying foxes are suffering for it.

"A lot have to be put down over time due to the severity of the injuries getting worse," she says.

While man-made contraptions pose an ongoing risk, the warming climate could threaten the vulnerable flying fox's very survival.

When temperatures soar above 40 degrees, they become stressed and can die off in large numbers.

"There's physiological limits in terms of how much energy they're using and how much water they need," says Dr Pia Lentini, a senior scientist at biodiversity research organisation the Arthur Rylah Institute.

"When they're pushed beyond those limits, they become quite distressed. They'll start flapping and licking their wings and slowly moving down the trees.

"We know our climate is changing and we're experiencing more extreme weather events, so we may start to see an increasing number of these heat stress events."

If the flying foxes, who also underpin ecosystems via seed dispersal, become more vulnerable it could pose a risk to other native flora and fauna.

"Any time we take a species out of the system, the system has to work really hard to rebound," according to RMIT University researcher and bat expert Casey Visintin.

"In some cases, it changes altogether into a state that may or may not be desirable."

More sprinklers have been installed at Yarra Bend Park and other roost sites across Victoria to cool the vulnerable animals.

Friends of Bats and Bushcare are also improving Yarra Bend to make it safer for them.

They complete regular revegetation works and support Fly By Night in their soft release program, where hand-reared flying foxes are returned to the colony.

The bats are kept in the release cage for about 10 days before slowly moving back into the trees, says Friends of Bats and Bushcare secretary Megan Davidson.

"We continue to feed them for about six weeks, gradually reducing the amount of food we're giving them.

"That gives them time to develop their own skills in flying out with the rest of the wild bats."

Neither Dr Davidson nor Ms Hogarth have formal veterinary science or conservation qualifications but their passion for the flying foxes drives their volunteer work.

They also passionately defend the Yarra Bend colony, which has copped a bad wrap from residents for its loudness and strong smell, including calls by former Liberal MP Tim Smith for a cull in 2020.

But Dr Davidson says it's important to protect the animals she fondly calls "sky puppies".

"This is an ancient species that has been on this continent for millions of years," she says.

"You're looking at a little slice of prehistoric Australia when you're in a bat colony."

Australian Associated Press