Why are all the bats dying?

The moon sits high in the sky; uncloaked by cloud, the fullness of its shape is mesmerising. The shadow of wings stretched in flight can be seen as a bat passes overhead. It’s followed by another and yet another. Wings swoosh. Their distinct echolocation click can be heard as they hunt. With bats found everywhere besides the Arctic, Antarctic and a handful of islands in Oceania—this is a familiar nightly sight world over.


Why are all the bats dying?

By Fiona Murphy


From the burrowing bats of New Zealand, with their lumbering gait, to the South American vampire bat, whose name is far more menacing than its nature— there are over 12000 species of bat. This roughly accounts for 25% of all mammal species. According to the IUCN Red List, nearly half of the bat species are under threat. Why are bat populations declining? Dividing deeper into this issue, it becomes quickly apparent that the causes are just as diverse as the number of bat species that exist.


Millions of bats in eastern North America are dying, in some regions less than 10% of bat populations remain. Bats are becoming infected with a fungal disease called white-nose syndrome (WNS). According to researchers WNS ‘is one of the most rapidly spreading wildlife diseases ever recorded’. The condition has been responsible for the death of approximately 6 million of bats since 2008. WNS has been diagnosed in seven bat species living across 26 US states and 5 Canadian provinces, and it’s spreading. In March 2016, WNS was discovered by hikers 30 miles east of Seattle.

“We are extremely concerned about the confirmation of WNS in Washington State, about 1,300 miles from the previous westernmost detection of the fungus that causes the disease,” said U.S. Fish and Wildlife Service Director Dan Ashe in a press release.

“Bats are a crucial part of our ecology and provide essential pest control for our farmers, foresters and city residents, so it is important that we stay focused on stopping the spread of this fungus.”

It appears that WNS disrupts the winter hibernation cycle of bats roosting in damp caves. Bats typically spend most of their hibernation in deep torpor, a state during which their body temperature is less than 10°C. Periodically, when the ambient temperature dips, their temperature rises to between 35 to 38°C. This process, called euthermic arousals, requires significant body fat reserves. The disease increases the period of time bats are spending in states of elevated body temperatures. Bats become emaciated and die. Or bats leave caves mid-winter to replenish energy stores, but because they are not equipped to deal with the harsh cold they perish.

WNS originates from Europe. However, differences in body composition and the speed of metabolic processes mean that European bats do not die from the fungal disease. So what is the cause of the decline in the bat populations in Europe?

Habitat Destruction

The rapid decline of the European species is not due to a fungal disease; instead, it is the overzealous approach to forest management. According to the report ‘Deadwood – living forests’, released by the World Wildlife fund: ‘Average forests in Europe have less than 5 percent of the deadwood expected in natural conditions.’ Up to a third of European forest species, including bats, depend on veteran and deceased trees for shelter and or food. Several bat species are on the decline because of the loss of hollow trees to roost in.

The report recognises that most efforts to clear deadwood in forests are due to several misconceptions including that it is: “a necessary part of “correct” forest management. Dead trees are supposed to harbour disease and even veteran trees are often regarded as a sign that a forest is being poorly managed.” These beliefs have resulted in some governments creating subsidies to encourage the salvaging of felled trees. However, this earnest and misguided human intervention means—“species relying on deadwood for food and/or shelter make up the single biggest group of threatened species in Europe”.

Daniel Vallauri, WWF Forest specialist, summed up the situation in a blog post: “Europe’s forests should be allowed to grow old gracefully. By stripping a forest of its decaying timber and old trees we are performing a strange and unnecessary cosmetic surgery on a natural ecosystem which threatens much of its biodiversity”.


The role bats play in biodiversity is often underestimated. The feeding habits of bats result in the pollination and distribution of seeds throughout an ecosystem. Without bat’s fulfilling this role, the biodiversity of a habitat swiftly suffers.

Despite the growing body of research relating to bats, misconceptions about bats still prevail. This can be clearly noted in the recent culling of Mauritian Fruit Bats.

Systematic Culls

The government of Mauritius approved the culling of Fruit Bats to commence in October 2015. The species was already listed as vulnerable on the IUCN red list. The bats were blamed for causing significant economic damage to the local fruit industry. Conservation organisations – Conservation International and WWF – opposed the cull of the protected species.

The Mauritian government’s decision to authorise the cull of an endangered species is unprecedented. Scientists criticised the methodology the government has employed to predict the size of the bat population. Mauritian Wildlife Foundation (MWF) estimates the population to be almost half what the government’s prediction, with the number of bats closer to 50,000. The proposed cull of 18,000 bats would wipe out almost 40% of the species. MWF cited recent studies indicating that bats are responsible for only 11% of crop damage. With “exotic birds and rats, as well as natural fruit drop and unharvested fruits” accounting for a greater proportion of lost yield.

The MWF have also criticised the government for not considering other solutions to manage fruit crops. Including training farmers to prune and net their trees. As well as considering alternate forms of harvesting such as an open access picking scheme, similar to a program the ‘Pick your own’ program operating in the UK.

What can we do?

The rapid decline of bats has scientists and environmentalists concerned. Without bats to control insect populations and act as key pollinators, ecosystems are set to be unbalanced.

The delicate interplay of fauna and flora is often underestimated. The effect of removing one component of an ecosystem, such as clearing deadwood, has far-reaching and often unpredictable consequences. Every environmental decision, from government policy to how you manage your backyard, has an impact. A world without bats, to control insect populations and pollinate habitats, would make for a very different and uncertain situation.

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