Thieving Bats

You’re taking your sandwich out of your lunch bag when the kid sitting next to you yells, “Look, an eagle!” Of course there’s no eagle, and when you get back to your sandwich, it’s gone. Bummer. Double bummer. What a nasty kid! Would it help if you knew that you’re not alone? Scientists Aaron Corcoran found that some Mexican free-tailed bats can be like the cafeteria bully.  

All bats hunt for food by broadcasting very, very high pitched sounds. These ultra sonic sounds are so high pitched, humans and most animals can’t hear them. The bats listen for the sounds to strike something—maybe a juicy moth, or a crunchy beetle—and bounce back to them. This is called echo-location. Dolphins use it too. Navy ships use it too—they call it sonar. They send out high frequency pulses, and listen to the bounce, the echo. Doing this, the bats, the dolphins and the captains of ships can “see” in the dark through the sound waves that bounce back to them. Have you seen a sonogram of a baby inside the mom’s tummy? Yep. Same thing.

Bats and dolphins use echolocation to zero-in on food. When a bat is closing in on the kill, they send out more and more signals, one right after the other. Scientists call this a “feeding buzz.” Aaron found out that when a Mexican free-tailed bat zeroes in and starts buzzing, a bully bat, sends signals at the first bat, as if they were echoes. The new signals jam and confuse the first bat, and then the bully sneaks through to get it’s dinner. But it’s not so easy as it would seem for the bully bat. Often the first bat sends its own jamming signals and they’re off in a high frequency duel to see who gets the food. 

How did Aaron figure this out? He was listening to Mexican free-tailed bats in Arizona using ultra frequency microphones. He heard something different. He and another scientist, William Conner, set up an experiment. They tied live moths to fishing line, and let them fly in the bat colony. When a bat started the feeding buzz, played the new call they had recorded. When they did this, the bats had a much harder time spotting the moth than when they didn’t play the recording.  Normally,  bats catch a prey two out of three times they hunt. With the recording, they only caught prey one out of every five times. These bats jam the communications of other bats just like in war soldiers try to jam each others’ communications.

Mexican free-tailed bats aren’t the only ones that  communicate about food. In an article in Smithsonian Magazine, Michelle Nijhuis talks about the big brown bat, a North American bat, which chirps to tell other bats they’ve got the rights to a bug. A European bat has sounds that warn other bats away from their area. These bats use their vocalizations to warn others away from their food, but they’re not bullies! 

I learned the information to write this article from National Geographic Magazine and from an article written by Michelle Nijhuis for Smithsonian Magazine.