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Researchers in Brazil credit the power of sound for scientific discoveries

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The Amazon rainforest is the most biodiverse ecosystem on the planet. Scientists there say the best way to experience it may be with your ears.

A MART?NEZ, HOST:

The Amazon is the largest and most biodiverse ecosystem on the planet. One of the best ways to really experience it may be to just listen to it. Researchers in Brazil credit the power of sound for leading them to scientific discoveries, including the world's loudest birds. With support from the U.N. Foundation, NPR's Kirk Siegler sent us this audio postcard from Camp 41 in Brazil.

KIRK SIEGLER, BYLINE: Ornothologist Mario Cohn-Haft's favorite time of day is just before dawn here on the equator. He can hear the jungle waking up.

(SOUNDBITE OF RAIN DRIPPING)

SIEGLER: Rain drips onto tree leaves the size of tennis rackets.

MARIO COHN-HAFT: You know, in a dark, tall, complexly layered rainforest, it's very hard to see creatures. And the real window into what's going on is sound.

SIEGLER: A chorus of tree frogs sings.

(SOUNDBITE OF FROGS CHIRPING)

SIEGLER: Other frogs hide in the leaf litter on the soaked ground.

COHN-HAFT: Yeah, it's singing right now. From the forest floor, it sounds like a cricket.

(SOUNDBITE OF FROG CHIRPING)

SIEGLER: Cohn-Haft works for Brazil's National Institute of Amazonian Research. He's been coming to Camp 41 since the 1980s. And almost all of the field studies he does here, trekking through this jungle surveying birds, are by ear.

COHN-HAFT: In the first half-hour of the day, we could hear 50 different species of birds and not see a single one.

SIEGLER: It's now 5:30, and the faint light of dawn is just beginning to peek through the towering canopy.

We have our headlamps on because it's still pretty dark, in case we step on a snake.

Channeling Indiana Jones - I mean, there was a viper sighting near the toilets last night. But no snakes we can see now anyway, just more exotic sounds, critters, parrots. It makes you feel like you're far away from everything.

COHN-HAFT: You just get so much information from hearing.

SIEGLER: Just by listening, Mario Cohn-Haft and his team recently discovered two never-before-known species of potoo birds. They also found what they believed to be the world's loudest bird, the white bellbird.

(SOUNDBITE OF SCREAMING PIHA CALLS)

SIEGLER: About a mile from camp, we stumble on its runner-up. This one's appropriately named a screaming piha.

COHN-HAFT: Stick with it for just a second, and I'm going to do something that you might find annoying (shouting) but. I'm just going to shout. And that usually gets them going. And the more we were talking, the more they were vocalizing. They are stimulated by loud noises.

(SOUNDBITE OF SCREAMING PIHA CALLS)

SIEGLER: Amazonian ornithologists get so used to the sounds, they can even tell what time of day it is just by listening.

COHN-HAFT: And believe it or not, there are actually a few species of Amazonian birds that I think of as old friends. They're species that I encounter regularly that I've never seen but that I recognize by their sound.

SIEGLER: There are more species of birds here than any other place on Earth.

COHN-HAFT: And that's the really fun thing about being in a species-rich tropical rainforest is that, obviously, discovering a new species is a real rush.

SIEGLER: For a reporter, just getting to be on a three-day overnight sleeping on hammocks in the heart of the Amazon is a rush, especially when it comes to hearing the howler monkeys.

(SOUNDBITE OF HOWLER MONKEY HOWLING)

SIEGLER: Their eerie, exotic howling, you could easily mistake them for the wind.

(SOUNDBITE OF HOWLER MONKEYS HOWLING)

SIEGLER: Then the monkeys go silent, and the rest of the forest is awake.

(SOUNDBITE OF BIRDS CHIRPING)

SIEGLER: Kirk Siegler, NPR News, Camp 41 in the state of Amazonas, Brazil.