Landing the spirit of the air: a team of scientists in Ecuador pursues a quest to monitor the endangered harpy eagle, one of the world's most powerful raptors.

• Author: Oxford, Pete
• Position: Cover story

A freshwater stingray wafted into the muddied murkiness of the Amazon tributary as we sloshed with unsteady footfalls, almost waist high in water, towards the gothic buttress roots of a giant kapok tree. Above me in the union of the majestic, bromeliad-covered branches of the emergent crown came the plaintive cries of a seven-month old harpy eagle--our quarry. Harpy eagles are rare and threatened throughout their range, and in Ecuador very little is known about them. Our mission: to attach a transmitter to the chick's back to allow us to monitor its movements over the subsequent three years.

Earlier we had awoken, as usual, in the dark at 4:30, crawled from our pup tents and, after a light breakfast, diluted by a heavy rain-forest downpour, we clambered, eight of us, into a failing dugout canoe. As Alex Blanco, the heaviest of our team both physically and in weight of experience, wedged himself into the last available space our freeboard compressed to less than an inch. We set off up the Pacuya tributary of the Aguarico River, a blackwater stream, sinuous with crowded and swampy borders, lined with a phalanx of thorns, vines, and verdant greens. It was a profoundly restful ride as we slipped in virtual silence toward the kapok, brimming with expectation and excitement this would be the day, we had decided; the day a harpy eagle we named Pacuyo (alter the river) would come down to earth.

We were in the Amazon rain forest of eastern Ecuador, close to the Colombian border in the Cuyabeno Reserve, bastion of the Cofan Indians. The principal members of our team were Oswaldo Criollo, a Cofan Indian who had first discovered the nest some two years previously and monitored it ever since; Ruth Muniz, a Spanish researcher who has studied harpy eagles in Ecuador since 2000; and Alex Blanco, a Venezuelan veterinarian and the only person in the world who captures harpy eagles in the wild. The rest of the contingent was there to manage the ropes, pull trap strings, or take photographs.

For the past eight days we had several times come close to capturing Pacuyo, yet still he evaded us. Now, under the tree for the ninth day in succession, tensions were high. It was the last day of our mission.

Named after a foul creature in Greek mythology, a half woman half bird who would snatch away the souls of the dead, harpies are the largest eagles in all the Americas and arguably the world's most powerful eagle. Adult males weigh nine to eleven pounds, while females are larger, at thirteen to twenty pounds; wingspans of the largest harpies can reach over six feet.

To the Huaorani, a native Ecuadoran...