Lending Sonoran Desert Bats an Ear
STEVE INSKEEP, host:
Think of that as a translation of the sound that bats use to navigate. They send out calls that bounce off objects and come back to their super-sized ears. It's like sonar. Now, different bats make different sounds, and those differences are helping scientists to identify and protect bats.
Here's NPR's Ted Robbins.
TED ROBBINS: This is what most bat calls sound like to us.
(Soundbite of silence)
ROBBINS: Silence. That's because many bats echolocate in frequencies far above the range of human hearing. But if you use a device called an Anabat detector and lower a bat call from around 80 kilohertz down to 18 kilohertz where we can hear it, it sounds like this.
(Soundbite of bat call)
ROBBINS: Still a series of indecipherable clicks. That's because a bat call is not only high - it's fast. Each click is maybe 8 to 12 milliseconds long. So biologists like Debbie Buecher use a second device.
Professor DEBBIE BUECHER (Biology, Missouri Western State College): This is the time expansion. So it takes it and it slows that call down and drops it in frequency.
ROBBINS: To where it sounds like, well, you decide. This is the slowed down call of a big brown bat.
(Soundbite of slowed bat call)
Sounds like a birdcall, doesn't it? As birds and bees do, bats pollinate plants. Bananas, cashews, even the giant Saguaro cactus might not exist without them. Bats also eat gobs of night-flying insects like mosquitoes.
But bats, Debbie Buecher says, evolve their calls for very different reasons than birds.
Prof. BUECHER: The natural selection for a birdcall is to attract a mate. But for a bat, the call is to avoid obstacles, not run into the wall, and to catch a prey item that is flying in the air that's trying to get away.
ROBBINS: Which brings us inside Kartchner Caverns State Park in southern Arizona, where Debbie Buecher and her colleague Ronnie Sidner studied a colony of Cave Myotis bats which roost here. Normally, they'd have captured, examined, and released the bats using low-hanging mist nets - fine mesh the bats get caught in. But Ronnie Sidner says even that seemingly modest disturbance could damage this colony.
Ms. RONNIE SIDNER (Bat Researcher): It is a maternity site. So females of this species come here and give birth. If you drive a mother away, her pup will die, because no one else will feed her pup.
ROBBINS: So they set up Anabat detectors and left them to record the bat calls. When they listened, they learned when the bats were active, where they went, and what they did.
Outside the cave, Debbie Buecher says recordings can sonically capture more species and more individuals than a net can, species that fly high, for instance. What these and other bat biologists have found is that different bats have different calls. Here's a Yuma Myotis bat.
(Soundbite of Yuma Myotis bat call)
ROBBINS: And here's a pocketed freetail bat.
(Soundbite of a pocketed free-tail bat call)
ROBBINS: The different calls can tell scientists what species live in which parts of an ecosystem. Now, here's a Western Pipistrelle. Listen to how it starts slow, then gets faster as it catches an insect.
(Soundbite of Western Pipistrelle bat call)
ROBBINS: Turns out that pattern is common to all bats. When they talk, bats differ between species; when they eat, they all sound the same. Pretty much like people.
Ted Robbins, NPR News.
INSKEEP: This is…
(Soundbite of bat call)