STEVE INSKEEP, host:
Think of this next report of the triumph of the little guy. In this case the little guy is a moth. A species of tiger moth in the Southwestern United States apparently learned to confuse a dangerous predator.
Bats are among nature's cleverest predators, using ultrasonic signals to locate their prey at night. They make quick work of moths. But just as guerilla fighters find ways to evade the superior technology of a large army, one species of tiger moths seems to be jamming the signals of enemy bats. NPR's Christopher Joyce reports on an ultrasonic aerial war.
CHRISTOPHER JOYCE: In the bat-eat-moth world of the summer night, moths are at a distinct disadvantage. Bats can locate and snap up a moth out of midair with the greatest of ease. They use what biologists consider to be one of the animal world's most efficient tools of prey: ultrasonic signals that work like sonar.
But Aaron Corcoran, a graduate student at Wake Forest University, was intrigued by a species of moth that also makes ultrasonic sounds. He wondered if this was some kind of bat deterrent. The moth, an orange species with a four-inch wingspan called Bertholdia trigona, has organs on its body called tymbals.
Mr. AARON CORCORAN (Wake Forest University): This tymbal kind of works like a pop can, that if you push in on the side of a pop can, it will make a click, and then as it releases out it makes another click. We've measured up to 450 clicks in a tenth of a second. That's a tremendous amount of sound that this moth is making.
JOYCE: Corcoran removed the tymbals from some of these moths and then tethered the insects - that's right, tethered them - with fishing line, so they could fly, but not too far. He brought in a bat and filmed what happened. The sounds have been slowed down so the human ear can hear them.
Mr. CORCORAN: As a bat is flying around, it's constantly making chirps and listening for the echoes.
(Soundbite of chirping)
Mr. CORCORAN: And as it closes in on the insect, it increases the repetition rate with which it's making those sounds.
(Soundbite of chirping)
JOYCE: The tethered moths, the ones that could not click, got eaten. No problem at all for the bats. So what about an intact moth with its tymbals clicking away as the bat closes in? Corcoran tethered up some of these moths.
Mr. CORCORAN: You hear the bat going through its normal progression and then starting to speed up. And then the moth turns on its sound production, which sounds almost like a siren because the pitch is going up and down. At that point the bat does something very abnormal: it starts slowing down its repetition rate, the opposite of what it would normally be doing.
JOYCE: Here's what it sounds like. The rattle-like sound is the moth clicking.
(Soundbite of chirping and clicking)
JOYCE: As soon as the rattle started, the bat got confused and missed the moth. This kept happening, over and over, until the bat finally gave up and crawled back to its cage.
Corcoran, who published his findings in the journal Science, ran the experiment several times with the same results. He's ruled out the idea that the sound just startles bats. The bats would have grown used to that and eventually had more success. Corcoran and his colleagues think it's some kind of ultrasonic jamming.
Mr. CORCORAN: What appears most likely is that the clicks are interfering with the bats' neural processing of the echoes that are coming back.
JOYCE: Corcoran says if you live in the southwestern U.S., you just might catch some of this aerial action underneath a streetlight at night.
Christopher Joyce, NPR News.
(Soundbite of music)
INSKEEP: To see a high-speed video depicting a moth jamming a bat's sonar you can visit our Web site today at NPR.org.
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