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RENEE MONTAGNE, HOST:

It's MORNING EDITION from NPR News. I'm Renee Montagne.

(SOUNDBITE OF A TOUCAN)

MONTAGNE: Brazil is a paradise for birds. You're hearing some now. It's a country with more than 1700 species, among them the colorful toucan...

(SOUNDBITE OF TOUCANS)

MONTAGNE: ...a bird with an almost comically giant bill that can be half as long as its body. There are lots of different kinds of toucan: red-breasted, channel-billed, keel-billed, each with its own color-scheme and distinctive call.

(SOUNDBITE OF TOUCANS)

MONTAGNE: Unfortunately, as more humans have moved into Brazil's forests, the number of toucans has dwindled.

And as NPR's Christopher Joyce reports, scientists now notice that the downfall of the toucan has created an unexpected evolutionary change in the forests.

(SOUNDBITE OF TOUCANS)

CHRISTOPHER JOYCE, BYLINE: Walking through the Atlantic coastal forests of Brazil in the morning is like eavesdropping on a toucan symphony. Each produces its own unique sound to cut through the auditory clutter. But over the past century, the toucans have been disappearing. Hunting, farming, logging - it's taken a big toll on toucans.

With fewer and fewer birds, the toucan symphony is down to a murmur. They're just about gone from many parts of the forest. And it appears that their disappearance kick-started a whole evolutionary change in the forest itself, particularly in its palm trees.

According to research in the journal Science, this is what happened. The dominant palm tree depends on birds to eat its fruit and then defecate the seeds somewhere, so it will germinate and grow a new tree.

Mauro Galetti is a biologist at the Estadual Paulista University in Brazil. He says toucans play a big part in this reproductive process.

MAURO GALETTI: These large birds, they have an extremely important role in the forest not only because they disperse seeds, but because they disperse large seeds.

JOYCE: The largest palm seeds, some the size of marbles, are too big for most birds to eat except for those big-mouthed toucans. So as the toucans disappeared, the palms that made big seeds were out of luck - no seed dispersers. Meanwhile, the palms that were genetically disposed to make small seeds did just fine; in fact, they thrived and started to dominate the forest.

GALETTI: The extinction of large birds changed the evolution of this palm.

JOYCE: Now, humans have always been messing with nature. When we cut down forests or prairie, or when we over-hunt, we change the mix of plants and animals. But in this case, humans actually altered the genetic makeup of a wild palm tree population, in just a century, by accident.

So what happens if these small-seed palms eventually take over? Well, it turns out that smaller seeds aren't so good. They dry up and die faster in hot, dry weather. And scientists predict that climate change will make parts of Brazil hotter and Drier, so much so that these palms could be in trouble.

GALETTI: The impacts on the forest can be quite dramatic because several animal species depends, rely on this palm for food.

JOYCE: About 60 species of animals, in fact. So the take-home message is: As the toucan goes, so goes the forest.

Christopher Joyce, NPR News.

MONTAGNE: Our toucan vocalizations came from the Cornell Lab of Ornithology's Macaulay Library.

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