Bats are dying en masse, and nobody has really done enough to stop this disturbing trend. Now, researchers have published the results of a new worldwide review that looks closely at the reasons why. It turns out the threats to bats have changed dramatically over the last five decades.
The team, partly based in Fort Collins Science Center, put together a database, counting any place where ten or more bats were reported dead in a short time—up to a year, but usually "within a few days or a season." They recorded 1,180 multiple mortality events (MMEs) and divided them into nine categories. The results show how the threats to our cute nocturnal friends have changed over the decades in ways that mirror the overall environmental changes in the world.
Before 2000, the biggest danger for bats was intentional killing by—you guessed it—humans. In North America and Europe, we killed them because they were a nuisance. In South America, we didn’t like vampire bats. In Asia and Australia, bats ate too much fruit, and in Asia and Africa, we ate the bats. In total, from 1790 to 1999, 39% of MMEs were due to intentional killing by humans.
After 2000, the killing got less intentional, but much more effective. The major threats to bats since then are white nose syndrome and wind turbines. White nose syndrome, which sounds like something a 1980s yuppie might suffer from, is in fact a fungal growth that attacks a bat’s wings and muzzle while it hibernates. It has killed between 6 and 7 million bats to date in North America, eliminating up to 90% of some species within five years of outbreak.
From 2000 onwards, 35% of MMEs have been caused by collisions with wind turbines, although this figure may be "biased by regulatory reporting requirements in North America and Europe," says the report. Another 35% of deaths were due to white nose syndrome. The researchers estimate that "these two causes will probably soon outnumber all prior reports from all categories combined." And it’s just going to get worse. "Storms, flooding, drought, and other abiotic factors also cause mortality, and are likely to increase with climate change," says the report.
In light of the already-precarious status of the bat population, and the likelihood of more threats in the future, the team recommends "policy, education, and conservation actions targeting human-caused mortality." At the very least, we can try to find better ways to stop killing them with our climate change solutions.