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Animals burn a lot of energy during long-distance migrations. New research in the journal Science suggests some bats make their journeys a bit easier by getting a lift. Here's NPR's Jonathan Lambert.
JONATHAN LAMBERT, BYLINE: Bat migration is a bit of a black box. Unlike many birds and other migratory species, bats only fly under cover of darkness. And that's made them harder to study, says biologist Edward Hurme.
EDWARD HURME: So they're fast, and they move at night. And once they disappear from an area, we don't necessarily have the ability to figure out where they show up somewhere else.
LAMBERT: To overcome these challenges, they needed a way to track the bats. While GPS tags have helped researchers follow bird migration, bats are pretty small, so traditional tags don't quite work.
HURME: To have something that can remotely send data about an animal and be small enough for a bat is really hard to come by.
LAMBERT: So Hurme and his colleagues at the Max Planck Institute of Animal Behavior in Germany got creative. They study a species called the noctule bat that migrates across Central Europe, traveling northeast from around Switzerland towards Poland in the spring. To track their migration, they designed special tags small enough to fit on the bat's back, sort of like a little backpack.
HURME: So the tags are really cool. They have multiple sensors on them, so they can record temperature and acceleration. And they don't actually have a GPS on them at all.
LAMBERT: Instead, the tag connects to a wireless network, sort of like how a cellphone does. That allows the researchers to track their migrations in unprecedented detail. They followed over 70 bats and got some pretty surprising results.
HURME: We found that a lot of bats are actually migrating before storms come through. And this will generate some strong winds that are typically blowing in the right direction for migration. And bats typically try to ride this storm front.
LAMBERT: In other words, the bats are timing their departure to leave just before a storm comes through. Deciding to leave right when these winds arrive can save bats a lot of energy on their journeys, which can span nearly a thousand miles.
HURME: Sometimes they can ride it for one or two nights. But usually, the storm keeps moving during the day, and so while the bats are sleeping, the storm keeps going. And then they have to wait for the next good opportunity to migrate.
LAMBERT: Waiting too long for the perfect winds has a cost, too. Female noctule bats are usually pregnant this time of year. And the longer they wait, the heavier their little bat bun in the oven will be, which could weigh them down.
HURME: It's kind of a gamble when and where to migrate.
LAMBERT: But more fully understanding the bats' journeys could ultimately help their conservation. Wind turbines, for instance, can kill a lot of bats. And Hurme hopes this work might help researchers develop migration forecasts that energy companies could use to minimize harm to these nighttime fliers.
Jonathan Lambert, NPR News.
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