The Yellow-billed Continga is among many species in danger of vanishing before anyone learns fundamental facts about them.

THE GIST

- Scientists have managed to put radio transmitters on three Yellow-billed Cotinga, an extremely rare Costa Rican bird.

- Only between 250 and 1,000 of these birds remain, yet scientists still don't know basic facts about them.

- Learning where the birds go and how they live will help researchers protect entire ecosystems that are in peril.

Karen Leavelle stood in the dusty parking lot of a riverside restaurant in the rural town of Rincón, on the remote Osa Peninsula in southern Costa Rica. She held a six-pronged, mini golf club-sized contraption above her head, and scowled toward the treetops.

At 7:45 in the morning, it was already blisteringly hot in the shade. Nearby, construction workers stared at the small, pony-tailed woman and her odd equipment, even though they see her and co-investigator Luis Vargas there every day. Other workers toiled on the road with cranes and diggers to replace a rickety old bridge over the Rio Rincón with a sturdier one.

Drilling noises mingled with the hooting of birds, the buzzing of insects and some clanking sounds from the mostly empty bar and restaurant Montaña Rio. But Leavelle tuned it all out.

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She was listening for something else -- the telltale blips that would reveal the locations of three elusive birds equipped with radio-transmitting harnesses. Known as Yellow-billed Cotingas, the birds live only in this tropical corner of the world, and their species may contain just a few hundred individuals, making it perhaps one of the rarest species in the world.

In mid February, a few hundred meters down the riverbank from the restaurant, Leavelle and Vargas managed, for the first time, to both catch the birds and wrangle them into harnesses. Now, the researchers are racing to learn the basics about the species -- from what habitats they are using year round and how far they fly to where they go as the seasons change. They are also looking at reproductive and feeding behaviors that are still unknown to science. Sometime in the fall, the radios will stop working.

As the researchers gather information, their goals reach beyond a single endangered bird in a remote region of Central America. The plight of the Yellow-billed Cotinga represents the challenges facing a whole slew of plants and animals that, like this bird, depend on mangroves and adjacent rainforest as well as other threatened habitats. Many creatures are in danger of vanishing before anyone ever learns the most fundamental facts about them.

"Information obtained through scientific study is limited for this species," said Leavelle, an ornithologist with Friends of the Osa, a U.S.-based conservation organization that works in Costa Rica. "Continued study of the Yellow-billed Cotinga will help toward creating a conservation plan for this endangered bird and the mangrove rainforest ecosystem it depends on here in its restricted tropical range."

"A lot of mangroves and adjacent rainforest have been destroyed," she added. "This system in Rincón is very small, and we hope to keep it protected."

Yellow-billed Cotingas are dove-sized birds that have a regal and peaceful air, said Ken Rosenberg, director of conservation science at the Cornell Lab of Ornithology in Ithaca, N.Y.. All have yellow beaks, but females have grey feathers, while males come in a snowy shade of white.

The birds spend most of their time high up in the tops of trees. They move in small groups. They mainly eat fruits and possibly insects. To court mates during the breeding season, males perform fancy flying maneuvers, swooping from one leafless branch to another. And that is basically the extent of what scientists know about the Yellow-billed Cotinga.

Otherwise, the species is mired in unknowns. Many details about its life history are missing. Researchers aren't even unsure of its population size. BirdLife International estimates that there are probably fewer than 1,000 of the birds left, but there may be fewer than 250.

No one knows how much the bird's population size has declined over years, either, though the Yellow-billed Cotinga was probably rare to begin with, originally ranging from the central Pacific coast of Costa Rica to the central Pacific coast of Panama. Because the birds depend on mangroves, their numbers are likely shrinking.

Mangroves around the world are under siege from development and changes in sea level, Rosenberg said. And it's not just the Yellow-billed Cotinga that is suffering as a result. Mangroves also provide coastal refuges for many birds -- both resident and migratory -- and for baby fish and other sea life.

Like the yellow-billed Cotinga, many tropical birds are highly dependent on a single kind of habitat, Rosenberg said. Many of those habitats are in peril, too. And many of those birds remain mostly unstudied.

"Something like a flashy bird becomes a flagship," Rosenberg said. "It represents a whole ecosystem. It's not really just about saving the Cotingas. It's a vehicle for saving the habitat that is critical for a lot of migratory birds that go down there in the winter."

After a few blips on her receiver, Leavelle plunged down a set of steps from the parking lot to the riverbank, then walked along the edges of the trees. Along the way, she looked up with a sense of urgency. Leavelle has come to this spot along the Rio Rincón every day since early January, when she and three colleagues began their attempts to catch Yellow-billed Cotinga by hoisting nets high up into the canopy.

It took them six weeks, but in mid-February, the researchers finally caught three birds in three consecutive days. Now, the conservation community is counting on two white males and a grey female bird to reveal the secrets of a small, but critical species.

"Look, there's one!" she said. "Two females, flying across the sky!"

It was the closest glimpse she would get that morning of a bird that is poised to help protect the biodiversity of an entire region.