Migratory bats ride storm winds to speed their journey: NPR

Historically, bat migration has been a bit of a black box. While scientists have learned a lot about how birds migrate, the few species of bats that take long journeys are more difficult to study.

“They are fast and move at night,” says Edward Hurme, a biologist at the Max Planck Institute for Animal Behavior in Germany. “Once they disappear from one area, we don’t necessarily have the ability to determine where they reappear elsewhere.”

Bats are also smaller than many migratory birds, meaning the tracking tags researchers stick to birds are too heavy for bats.

“It’s really hard to find something that can remotely send data about an animal and that’s small enough for a bat,” Hurme says.

So Hurme and his colleagues had to design one. They created specialized tags weighing just over a gram that measured the animal’s movements as well as its temperature. Unlike other tags, which measure animal movements but must be retrieved by scientists to download the data, these new tags broadcast their information over a wireless network, in the same way as a cell phone. This allows researchers to triangulate their position and follow the bats’ path.

In total, the team equipped 71 female noctule bats with these sensors. In spring, females typically migrate from their hibernation grounds in Switzerland and Germany to the northeast, where they roost. When the researchers combined their tracking data with climate data, they noticed a curious connection.

“We found that many bats migrate before storms hit,” says Hurme. In spring, storms are usually preceded by warm fronts that generate strong winds that generally blow in the right direction for migration. This translates into significant energy savings for the bats, says Hurme, which can migrate nearly 1,000 miles.

It turns out that these noctule bats time their spring departure to coincide with the warm fronts that precede storms, Hurme and his colleagues reported this week in the journal. Science. These winds tend to blow in the general northeast direction of bat migration this time of year, giving the bats – which weigh about an ounce – significant lift.

“It was actually a big surprise. We had some clues that bats responded to good wind conditions, but we didn’t think there was this connection with storms,” ​​says Hurme.

“Sometimes they can travel through it for one or two nights, but usually the storm continues to move during the day. So while the bats are sleeping, the storm continues. And then they have to wait for the next good opportunity to migrate “, explains Hurme.

There is, however, a cost to waiting too long. Many of these females are pregnant, and the longer they wait, the heavier they will be. Plus, the winds can always change.

“At the end of last year, the last bat to migrate was a week later than all the others,” says Hurme. “But the wind direction completely changed to blowing south, and it finally gave up and migrated against the winds.”

Researchers have not yet discovered what signals bats use to time their departure. More broadly, Hurme hopes more research groups will start using the tiny bat tags on other bat species.

“We are working with colleagues from Spain to the Czech Republic and trying to fill in the gaps of what bats do across the region as they fly north in the spring and return south in the fall .”

Ultimately, this type of work could help conserve bats. Collisions with wind turbines, for example, kill many bats. Understanding when and where they migrate could help researchers develop bat migration forecasts, which could help energy companies turn off turbines during migration, or avoid building in certain areas altogether, he says.

“We have a long way to go, but I hope we can start to move toward a better system for predicting exactly when and where bats are expected to migrate.”