ANTHONY BROOKS, host:
Back now with DAY TO DAY.
Right now, you're using your ears to hear me. But animals send signals to each other by making things vibrant, things like twigs or leaves or the ground itself.
It's called seismic communications, and it's a growing field of study for biologists.
Jeff Rice brings us a sample of this new sound science from this month's Acoustical Society of America Conference in Salt Lake City.
JEFF RICE: You might compare it to the period in the 1950s and 1960s when amplified music took off. That era spawned a modern electric guitar, and nothing was ever quite the same.
(Soundbite of song, "The Star-Spangled Banner")
RICE: Now biologists are plugging in, using equipment like lasers, electrical pickups and geophones to amplify previously hidden and unknown vibrational signals between species.
(Soundbite of vibrational signal)
Typically, humans can't hear these sounds in the air, and this hidden world of vibrational communication prompts people like Dr. Rex Cocroft of the University of Missouri to go what he calls acoustic prospecting.
Dr. REX COCROFT (Researcher and Professor, University of Missouri): You could go down to a local music shop and buy an amplified speaker and a guitar clip -pick up and go on clip onto a plant, and you might hear nothing or you might hear something that nobody's ever heard before.
(Soundbite of vibrational signal)
RICE: Cocroft estimates that there are at least 200,000 different insect species that communicate through vibrational channels. Some of his favorites are the leafhoppers.
(Soundbite of vibrational signal)
Dr. COCROFT: And you just never know you might put some, rather, undistinguished looking little insect on a plant stem and record its vibrational signal, and it might be very boring or it might be something that just knocks you off your chair, and you think, no. This is ridiculous. And you just burst out laughing.
(Soundbite of vibrational signal)
RICE: To illustrate his point, Dr. Cocroft sent me some of his most recent recordings, made just for this broadcast. He attached an old phonograph cartridge to the grass in his backyard in Missouri. And within a few minutes, he'd recorded these sounds, which even he had never heard before.
(Soundbite of vibrational signal)
Dr. COCROFT: It can be quite fun to just walk around, you know, the edge of the woods or out on the meadow and clip onto a plant where you might or might not even see any insects on it, and you just hear this enchanting set of sounds.
(Soundbite of vibrational signal)
Dr. COCROFT: And even in the grass in your lawn, if you look down, you'll see insects scattering onto the sides and the leafhoppers flying out. But that's where they're hanging out and that's where they're signaling. So your lawn is actually a whole network of pretty interesting signals.
(Soundbite of vibrational signal)
RICE: For NPR News, I'm Jeff Rice.
(Soundbite of vibrational signal)
BRAND: Now, here's a quiz. What's the difference between an insect and an elephant? It turns out, not as much as you think. Dr. Caitlin O'Connell-Rodwell of Stanford University was first an entomologist and studied plant hoppers and vibration communications in plants.
(Soundbite of growling elephant)
Dr. CAITLIN O'CONNELL-RODWELL (Ecologist, Stanford University): The image for me of an insect freezing and the leaning forward and sometimes lifting a foot off when they're listening for another insect - I had that image in my mind when I went to Africa and started studying elephants and saw that elephants were doing the same thing. Before the arrival of another herd, they would suddenly freeze and lean forward unto their front feet and then lift one off the ground. And I thought, well, that's so similar to the insects that I can't believe it. It looks like they're actually listening for ground vibrations.
(Soundbite of growling elephant)
Dr. O'CONNELL-RODWELL: When we played back these vocalizations to elephants for the first time and saw them freezing and then, you know, a whole group of elephants - 15 to 20 individuals - all freezing, then leaning forward unto their front legs - and they weren't scanning in the air with their ears, unless they would if they heard an acoustic signal. But they were really focused on the ground and paying attention. I just - I couldn't believe it, I was so excited.
(Soundbite of growling elephant)
Dr. O'CONNELL-RODWELL: Well, elephants create a very low frequency vocalization called a rumble, and that vocalization's create at about 20 hertz.
(Soundbite of growling elephant)
Dr. O'CONNELL-RODWELL: And it's created with such a high amplitude, it's like a little explosion - that it goes into the air but it also couples with the earth and becomes the surface of the earth, so it's a ripple. It's like an earthquake. If you think about parking lots and bridges breaking up in an earthquake, elephants are feeling these ripples and discriminating between different ripples.
Soundbite of growling elephant)
Dr. O'CONNELL-RODWELL: Elephants hear through their feet through two potential different pathways. They can hear - they can detect vibrations through vibration sensitive cells in their feet or through bone conduction, through their bone - their foot bones and into their middle ear. You wouldn't think this, but they're actually walking on their tiptoes. They have a huge fat pad that their feet rest on, and that fat pad is very dense fat. It's a lipid fat that's very similar to the dolphin melon and marine acoustic fat, so what - we think that that fat is facilitating the coupling of vibrations from the ground environment into the elephant.
Soundbite of growling elephant)
BRAND: That was Caitlin O'Connell-Rodwell - not the elephant - of Stanford University. Our stories on the way elephants, insects and plants use vibration to communicate were produced by Jeff Rice. They come to us from the HearingVoices Radio Collectives.
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