More on Bairnsdale’s Bat Die-off

A trailer load of carcases (image Shelly Nundra)

Our local throwaway the East Gippsland News (EGN) headlined the recent flying-fox die-off on the front page of the January 30 edition with ‘Bats overcome by Heat’. The EGN quoted police sources that the “incident had been declared a ‘natural emergency’” and that the “bats are diseased”.  Its emphasis was on a ‘natural emergency’ and ‘natural event’. An opponent of the Bairnsdale colony was interviewed without balance from Bairnsdale Friends of Bats and Habitat Gippsland group. There was no mention of the fact that clear-fell logging had reduced both their roosting sites and food supply. Climate change was not mentioned.

There is some basis of fact in the official statements and actions both with regards the ‘natural’ aspect of the event and ‘disease’. But both are misleading in the extreme and the die-off could at no stage be classified as a ‘human’ or ‘natural’ emergency. The police statement implied that all the bats were ‘diseased’ when in fact less than 1% of the bats in Australia carry the lyssavirus and as far as I am aware it has never been detected in the bats in the Bairnsdale colony. Further a bat carrying the virus has to bite someone to transfer the virus.

The probability of a death occurring as a result of lyssavirus from a bat is therefore extremely small and can hardly be called an ‘emergency’. The total number of known fatalities from lyssavirus in Australia is exactly three. So you have a far greater chance of being struck by lightning. On the other hand the increasing number of heatwaves making inroads into the flying-fox colonies are also killing humans. The heatwave that preceded and included Black Saturday caused an extra 370 fatalities in south-east Australia, some of whom, no doubt, were resident in Gippsland. So where is the real emergency to be found?

Whether the heatwave that caused the die-off was ‘natural’ is another matter. Whilst again it is true that we have had heatwaves before with climate change we are now experiencing them as longer, hotter and more frequent events. The temperature at which the bats begin to die is 42 degrees C. For human beings the temperatures at which we begin to die is less, especially when a heatwave over a number of days includes exceptionally high overnight minimum temperatures which prevents the body from recovering from the daytime heat. These temperatures are dry bulb temperatures.

I have written elsewhere in some detail about wet bulb temperatures. The thermometer that measures these temperatures has a wet cloth wrapped around the bulb and essentially it measures times of high temperatures with exceptionally high humidity. We start dying at wet bulb temperatures of about 30 degrees. Above 37 degrees because the body is unable to cool itself by sweating we all die without artificial cooling.

So the threat to human health is via climate change and the tragic demise of the Bairnsdale bats is another warning that our warming planet is more than an environmental problem or a ‘natural emergency’. It is an existential one. Whether we like it or not we are already in a climate emergency.