Flying foxes have been dropping off trees and dying in droves because of the effects of climate change, researchers say.

More than 30,000 of the fruit bats are estimated to have died since 1994 in heat waves associated with global warming.

Mass deaths from heat stress have occurred at least 19 times since 1994, as opposed to only three anecdotal reports of similar flying fox deaths before then.

The bats started to die as temperatures approached 42C, the study in Australia found. They are the first large mammal other than humans to be shown to suffer mass mortality during a heat wave.

Flying foxes, which can have a wing-span of 1.5 metres (5ft) and weigh more than 1kg (2.2lb), feed at night and roost in trees by day. Hanging upside down from branches rather than sheltering in caves or other cooler roosts leaves them exposed to the sun in the daytime.

Researchers said that as the temperatures rose the bats began making desperate attempts to cool down, first by using their wings to fan themselves and seeking shade in the trees, and then by panting and rubbing spittle over themselves.

After several hours in the baking sun, members of the bat colonies began dropping off the trees and were dead within 20 minutes.

Up to 13 per cent of black flying foxes, (Pteropus alecto) were killed by the heat in New South Wales and Queensland, according to the study, published in the journal Proceedings of the Royal Society.

Grey-headed flying foxes (Pteropus poliocephalus), of which there are thought to be just 400,000 left in the world, accounted for 24,500 of the deaths.

Britain’s bats tend to shelter in caves where it is cooler but other mammals are likely to overheat as temperatures in the UK hit the mid-40s later in the century, said Justin Welbergen, of the University of Cambridge, who led the study.

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