Bat Mortalities' Underlying Causes Revealed In New Study

A new study from the U.S. Geological Survey (USGS) has found that human influences may be driving bats to the brink of extinction. Wind turbine collisions worldwide and the rapidly-spreading disease known as white-nose syndrome in North America have led to numerous reported bat deaths since the start of the 21st century. These threats far surpass all prior causes of bat mortality.

"Many of the 1,300 species of bats on Earth are already considered threatened or declining. Bats require high survival to ensure stable or growing populations," Tom O'Shea, lead author of the study and a USGS emeritus research scientist, said in a news release. "The new trends in reported human-related mortality may not be sustainable."

Bats are long-lived, slow-breeding mammals that play vital roles in most of Earth's ecosystems: They help pollinate and disperse seeds in tropical regions and provide a natural form of pest control, many farmers cherish.

In the latest study, USGS researchers combed through data from 1790 to 2015 in search of annual mortality events involving ten or more bats. These "'multiple mortality events" were then divided into nine different categories, spanning a variety of both natural and human causes. In total, researchers categorized 1,180 events from all over the world, most of which can be traced back to human involvement.

Before 2000 it was common for humans to hunt bats for food, to protect their fruit crops and to control the population of vampire bats. Since the dawn of the 21st century, however, more bats have been found dead after flying into wind turbines or contracting white-nose syndrome.

Furthermore, extreme weather conditions are associated with increased bat mortalities, and could worsen with climate change.

Researchers suggest bats could greatly benefit from improved global policies, education and targeted conservation efforts.

"Determining the most important causes of bat mortality is a first step toward trying to reduce our impact on their populations," David Hayman, co-author and senior lecturer at Massey University in New Zealand, added.

Their study was recently published in the journal Mammal Review.

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