Ms Treadwell Kerr said volunteers managed to rescue about 850 animals but were stretched thin as they already had more than 500 flying foxes in care. "There had been a food shortage, which was probably due to the fact that it had been a very dry season and then they got the heatwave," she said. "In one camp [at Edmonton], the whole camp was wiped out, and 11,000 animals, at least, died. "And the flying foxes have not returned to that site yet even though since then we got a proper wet season for a change." Ms Treadwell Kerr said flying foxes were good "indicators" for climate change and their deaths were more readily noticed than other animals which may also be affected by extreme heat.

"When they die, you see it, it's right there in front of them," she said. "We were expecting it to happen at some stage – we weren't expecting it to happen in November." At one camp alone, volunteers found 11,000 flying foxes dead. Credit:David White In February, federal Environment Minister Melissa Price upgraded the spectacled flying fox from vulnerable to endangered on the national threatened species list. CSIRO research showed the population of the spectacled flying fox had more than halved from 214,750 in November 2005 to 92,880 in November 2014.

Macquarie University ecologist Tim Pearson said flying foxes were a keystone species, an important pollinator and seed disperser and vital for the health of forests. "One of the reasons flying foxes are so important, and this doesn't just apply to speccies [spectacled flying foxes], but other species in Australia as well, is they fly huge distances," he said. "So when they lick the nectar out of eucalyptus [trees], all that fur gets covered in pollen and then they fly 20 to 30 kilometres. "They pollinate the tree next to it but they pollinate trees far away so they ensure genetic diversity." Mr Pearson said the increased frequency of heatwaves had led to more mass die-offs elsewhere in Australia.

Almost 50,000 flying foxes perished during extreme heat in 2014 in south-east Queensland, while there have also been deaths in Adelaide and Victoria in recent months. About 850 spectacled flying foxes were rescued in far north Queensland, mostly pups. Credit:David White The Lab of Animal Ecology, led by Dr Justin Welbergen, reports mass casualties are occurring between zero to five times per year and the events are expected to escalate under climate change. "Where they used to be very occasional events, now they're happening more and more often," Mr Pearson said. "What was scary about the November instance in Cairns was that to the best of our knowledge, the spectacled flying fox, which just lives in north Queensland, has never been affected by heatwaves before ... They typically don't have heatwaves."

Mr Pearson said climate change meant days of extreme heat were becoming more frequent and more severe, which would lead to more flying fox deaths. Loading "Most of us who work with flying foxes ... are pretty convinced that their numbers are going to keep declining," he said. "The pressures on them are climate change and habitat destruction - neither of those two pressures shows any signs of slowing down." Official counts, revealed in Queensland open data, showed there were 1.4 million flying foxes of all species reported in the state in January to March 2016 and only 243,000 in January to March 2018.

However, a Queensland Department of Environment and Science spokesman said the data showed numbers from quarterly surveys of known roosts only and could not be used as an overall population estimate. This is because of the nomadic nature of flying foxes. Wildlife volunteers were stretched thin, as they were already caring for 500 flying foxes in care when the mass die-off occurred. Credit:David White The spokesman said the department recognised that recent heatwave events had significant impacts on flying fox populations. "Cyclones in north Queensland have also had a serious impact on flying fox food trees," he said.