The colony at Bendigo's Rosalind Park was as large as 20,000 bats in October, but Department of Environment, Land, Water and Planning records show there are only about 1300 bats left at the park.

DELWP Forest and Wildlife Officer Nicholas Ellis said it was normal for flying fox populations to fluctuate rapidly because of environmental factors like weather conditions and food availability.

But about 170 juvenile bats have died of heat stress in the past month, Mr Ellis said.

Flying fox expert and Friends of Bats and Bushcare group president Lawrence Pope said the changing climate was drastically affecting flying fox populations across the country.

Read more: Bendigo flying fox numbers surge 1000 per cent, prompting tree damage study

"We have lost about 4000 bats in Yarra Bend Park (in Melbourne) and more than 4000 in Adelaide," Mr Pope said. "It comes at a time when there is mass starvation and pup abandonment in NSW and Queensland.

"The grey-headed flying fox is suffering because of extreme weather conditions."

While heat stress events were natural, Mr Ellis said flying foxes were not equipped to deal with prolonged temperatures in excess of 40 degrees.

He said DELWP had been working with wildlife carers to assess and treat the distressed animals.

The City of Greater Bendigo has closed the fernery and one of the footpaths in Rosalind Park to limit the disturbance to the bats.

Fernery irrigation systems have also been activated to cool down the animals.

Mr Pope commended DELWP and the City of Greater Bendigo on their work to help the flying foxes. He said the public could also help in small ways.

"Removing nets around fruit trees is very, very important," he said. "Residents can cover part of the tree so they can keep some of the fruit for themselves.

"But the fruit in local backyards can allow the bats to re-hydrate and refuel. Also, we lose several thousands of bats a year because they get stuck in fruit tree netting.

"It is an easily preventable death. Never use a net that you can push your fingers through. It is not worth it."

Grey-headed flying foxes are listed as threatened under both state and federal acts. They are also protected under the Victorian Wildlife Act 1975.

Mr Pope said it was everyone's responsibility to ensure the Bendigo colony gets stronger.

Read more: Flying fox population could be Rosalind Park drawcard, City of Greater Bendigo say

"This is a species that we need critically for the regeneration of landscape and forest," he said. "Over 100 species of native trees require the grey-headed flying fox to regenerate.

"But there is a very real possibility that this species could be extinct before the end of the century.

"The role that places like Bendigo and Geelong are playing in helping the animals is absolutely solid gold.

"This is a conservation emergency and Bendigo and other parks are stepping up and doing their bit."

Mr Ellis said while Bendigo's bat colony was showing no new signs of heat stress, DELWP would continue to monitor the situation.

He said if people find a dead flying fox on the ground, they should not touch the animal.

People should instead contact DELWP, a local wildlife shelter, or the Wildlife Rescue Information Network to have the bat safely removed.

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