Sex And Death In The Rain Forest: A Matter Of Sound Scientists eavesdropping in trees have decoded a high stakes game of hide and seek. Katydids rely on ultrasound to find mates and listen for bats, which use ultrasound to find the bugs, and eat them.
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Sound Matters: Sex And Death In The Rain Forest

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Sound Matters: Sex And Death In The Rain Forest

Sound Matters: Sex And Death In The Rain Forest

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ROBERT SIEGEL, HOST:

Rain forests are noisy.

(SOUNDBITE OF ANIMALS VOCALIZING)

SIEGEL: There are insects, birds, maybe a howling monkey or two. But animals in the forest make sounds that don't show up in these recordings. NPR's Christopher Joyce and audio producer Bill McQuay from the Cornell Lab of Ornithology have been following scientists who've captured those sounds, sounds they say that determine who lives and who dies.

CHRISTOPHER JOYCE, BYLINE: Katydids can be an inch-long or the size of a cellphone. Many look like they're in Halloween costume with funny looking helmet heads or big horns. They also have an extraordinary talent that intrigues biologists...

BILL MCQUAY: As well as audio producers like me. What they can do is communicate ultrasonically at frequencies we can't hear.

JOYCE: At a lab at Dartmouth College, biologist Hannah ter Hofstede can actually show us evidence of this remarkable ability. She pins a katydid under a microscope then peels away the outer exoskeleton of its neck to reveal a pulsing clump of cells.

HANNAH TER HOFSTEDE: What you can see when you look through it in the very center between the two legs, there's a white blob. And that's like a mini-brain.

JOYCE: Ter Hofstede gently inserts electrodes the size of a hair underneath a nerve cell, a neuron.

TER HOFSTEDE: We play sounds to the ear of the katydid, and we'll be able to record with the electrodes when that neuron responds to the sound that we're playing back.

(SOUNDBITE OF BEEPING)

JOYCE: Katydid neurons are wired to hear ultrasound, but what for? Who's talking, and what's the message?

MCQUAY: So far, biologists know that male katydids use ultrasonic calls to attract potential mates.

(SOUNDBITE OF KATYDIDS VOCALIZING)

JOYCE: Hey, I'm over here. I'm over here.

MCQUAY: You might call it insect sexting, but there's much more going on ultrasonically than that.

JOYCE: Right. Bats use ultrasound, too. They emit signals like sonar to find prey. And they also hear ultrasonic signals.

MCQUAY: Dartmouth biologist Laurel Symes says that's bad news for katydids.

LAUREL SYMES: Katydids are the potato chips of the rain forest.

(SOUNDBITE OF BAT VOCALIZING)

MCQUAY: That's the sound of a bat homing in on a katydid.

(SOUNDBITE OF BAT VOCALIZING)

JOYCE: Katydids have a dilemma. Their mating calls are like dinner bells to bats. But they need to call to reproduce, so what's evolved in the rain forest is an ultrasonic game of hide and seek.

MCQUAY: Or seek and hide.

JOYCE: Yeah, seek mates but hide from bats. To figure out how it all works, Ter Hofstede sent a team into katydid country, a Panamanian rain forest where they actually recorded this ultrasonic world.

SHARON MARTINSON: All right, NPR, good morning.

(LAUGHTER)

MCQUAY: That's team member Sharon Martinson. I gave them a recorder to take with them. Martinson nicknamed it NPR.

MARTINSON: Throw NPR in, keep it rolling. Off to the furthest tree.

MCQUAY: The team has to plant special microphones in the forest to record ultrasound.

SYMES: You have to get a microphone in a tree. And so the first step of that is finding a good tree.

MCQUAY: You have to get a climbing rope up in the tree with an eight-foot long slingshot.

(SOUNDBITE OF SLINGSHOT SHOOTING)

SYMES: Oh, oh, oh, nailed it the first time.

(LAUGHTER)

SYMES: Well, (laughter) that doesn't happen all the time.

JOYCE: Symes climbs up into the canopy, which is already occupied by another primate.

(SOUNDBITE OF MONKEYS VOCALIZING)

SYMES: Here we are at the top. I can see monkeys from up here. Yeah, they're at the top of the next tree over.

NICOLE: All right, hoist her up.

MCQUAY: Symes hoists recorders, microphones and batteries up into the canopy and puts them in boxes for protection. Once she's back down, the monkeys reclaim the canopy.

NICOLE: Look up.

(SOUNDBITE OF MONKEY VOCALIZING)

NICOLE: Right there is a monkey. Oh, my God.

UNIDENTIFIED WOMAN: (Imitating monkey).

NICOLE: Going to go mess with our boxes?

UNIDENTIFIED WOMAN: Well, they're curious animals.

NICOLE: Oh, he's still looking at it.

JOYCE: They let the recorders run for days. When they listened back, it didn't sound like much, mostly crickets. But when the sound is slowed down, something haunting emerges.

(SOUNDBITE OF AUDIO SLOWING DOWN)

SYMES: This really low, continuous sound is the sound of crickets. These short, higher pitched sounds, the things that are two pulses...

(SOUNDBITE OF KATYDIDS VOCALIZING)

SYMES: ...Most of that's katydid calls.

(SOUNDBITE OF BAT VOCALIZING)

SYMES: The really high-pitched regular sound is the sound of a bat flying through. So each of those is an individual echolocation call that it's sending out.

(SOUNDBITE OF BAT VOCALIZING)

MCQUAY: And Ter Hofstede says their work has helped reveal how these insects have evolved to fool the bats.

TER HOFSTEDE: What I find the most interesting about the katydids is how much they have adapted to deal with these kinds of predators. So one of the things is that they don't produce very much sound.

MCQUAY: Some katydids only call for mates a few times a night.

JOYCE: So the bats can't home in on their location.

MCQUAY: Some apparently recognize a bat signal and go quiet when they hear it. Others just keep calling because they live underneath leaves and are harder for bats to find.

JOYCE: What's driving this ultrasonic arms race are hugely important evolutionary pressures - finding a mate and avoiding death.

TER HOFSTEDE: So what's cool about the katydids is that they're under these two extreme pressures. Each species may have found a different way to resolve that conflict.

MCQUAY: It's an arms race that's going on all the time out of sight.

JOYCE: But not out of hearing. I'm Christopher Joyce, NPR News.

MCQUAY: And I'm Bill McQuay, Cornell Lab of Ornithology.

(SOUNDBITE OF ANIMALS VOCALIZING)

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