Grey-headed flying foxes, listed as vulnerable, were the hardest hit, with volunteers recording thousands of carcasses at camps including Brimbank Park, Yarra Bend, and Tatura.

Wildlife Victoria and allied groups expanded emergency response, deploying a traveling veterinary service to key colonies amid concerns about national wildlife rescue capacity.

Mitigation ideas include installing sprinkler systems near affected colonies, with studies suggesting such measures can reduce bat deaths during extreme heat.

There are warnings that mortality could rise as heat continues to affect food sources, with potential long-term health issues like renal failure for survivors.

Outlets report hundreds to about 2,000 bat fatalities across regions, many of them babies or mothers, complicating recovery and rescue efforts.

Experts liken flying foxes to canaries in the coal mine, signaling broader ecological stress from ongoing extreme heat and climate change.

Heat reduced food availability by stressing bats and diminishing eucalyptus nectar, while direct heat and dehydration disproportionately affected mothers and pups.

In Illawarra, New South Wales, the event set a record for mass casualties, with 500 dead bats found at Brooks Creek and 170 at Figtree on January 10, and additional fatalities reported in Wolli Creek, Windsor, Parramatta, and Campbelltown.

Researchers warn of long-term conservation risks for vulnerable species and stress the need for improved wildlife rescue systems and resilience planning.

Public rescue efforts saved dozens of pups clinging to dead mothers, but many orphans will die without sustained care, underscoring strain on volunteers and the wildlife veterinary sector.

A severe heatwave across south-east Australia triggered the largest mass mortality event for flying foxes since the 2019-20 period, with thousands of deaths spanning South Australia, Victoria, and New South Wales.

Experts say temperatures above 42C drive bat mortality, and this occurrence is described as the most significant mass die-off since 2019-20.