Mirjam Guesgen
+64 6 951 7298
+64 21 740 414
M.J.Guesgen@massey.ac.nz
news.massey.ac.nz
Monday, January 18, 2016
Novel causes of bat death increase in 21st century
Embargoed until 4:30am (NZT), Wednesday, January 20, 2016
A comprehensive review lead by the United States
Geological Survey with Massey University, New
Zealand, Montana State University, United States
and the University of Glasgow, Scotland has
revealed trends in the occurrence and causes of
multiple mortality events in bats as reported
globally for the past 200 years – shedding new
light on the possible factors underlying population
declines.
The researchers combed the scientific literature
dating from 1790 to 2015 in search of mortality
events involving more than 10 bats per event.
They then divided these events into nine different categories, spanning a variety of both natural and
human causes. In the end, they found and categorised a total of 1,180 mortality events from all over the
world, representing more than 200 years of recorded history.
Collisions with wind turbines worldwide and the fungal disease white-nose syndrome in North America
lead the reported causes of mass death in bats since the onset of the 21st century. These new threats
now surpass all prior known causes of bat mortality – both natural or attributed to humans.
Prior to the year 2000, intentional killing by humans caused the greatest proportion of mortality events in
bats globally; the reasons for killing varied by region, but most commonly bats were killed as pests, for
food for people, for vampire bat control and to protect fruit crops. Although the proportion of intentional
killing declined in recent times, such acts still continue in some parts of the world.
In addition, storms, floods, drought, and other environmental factors also historically caused mass
mortality, and are likely to increase in the future due to climate change.
The reports authors say the findings are concerning because bats play vital roles in the ecosystem, such
as acting as pollinators or seed dispersers in tropical regions and insect control in most parts of the world.
Insect-eating bats are estimated to save farmers billions of dollars each year by providing natural pest
control. Also of concern, is that populations of many of the 1300 species of bats on Earth are considered
threatened or declining.
Lead author United States Geological Survey Scientist Emeritus Tom O’Shea says the trends in human
related deaths are not sustainable. “Bats need high survival rates to ensure stable or growing
populations.”
The authors did not find convincing evidence that bats regularly die in large proportion due to infectious
diseases caused by viruses or bacteria. This is perhaps surprising as increasing evidence points to bats
as natural reservoirs of several viruses that cause disease in humans. Despite often being more
gregarious than other animals, bats may somehow avoid diseases that sweep through dense populations.
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Co-author Dr David Hayman from Massey University’s Institute of Veterinary, Animal and Biomedical
Sciences says bats may somehow avoid large-scale mortality in spite of infection within dense
populations.
He says, “determining the most important causes of bat mortality is a first step toward trying to reduce our
impact on their populations.”
The researchers conclude bats globally could benefit from policy, education and conservation actions
targeting human-caused mortality.
The review was published today in the journal Mammal Review.
Dr David Hayman is available for interview. Please contact Mirjam Guesgen.
Image caption: Brown bats with white-nose syndrome.
Image credit: United States Geological Survey/photo by Nancy Heaslip.
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