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Swaddled in a sniper-style ghillie suit, Gabriela Tavera watched from the shadows as the blue-gray blur of the Harpy Eagle swooped in for the kill. Within seconds, the eagle’s enormous talons had eviscerated the opossum that Tavera had just released. The conservation biologist was wrestling with pangs of guilt over sacrificing one animal to feed another, but something changed when the raptor fixed her in its fearless, obsidian gaze. “I’d been an emotional wreck and was questioning the live feeding,” she says. “But at that moment, I realized it was for something much bigger.”

Tavera was feeding the bird as part of a project to which she and her colleagues had dedicated several grueling years: an effort to return a pair of rescued Harpy Eagles to the wild. In September 2023, their perseverance paid off with the first such rehabilitation of the world’s most powerful eagle in Bolivia—a triumph that, at times, seemed unlikely.

Balefully beautiful with its tyrant’s-crown crest, smoky plumage, and colossal claws, the Harpy Eagle once occupied a vast range that stretched unbroken from the tropical lowland forests of southern Mexico to northern Argentina. An apex predator perched precariously at the top of the food chain, the species was never very abundant; a breeding pair might need 20 square miles or more of healthy forest to find adequate prey and sites for nests, which they build in the canopy of the tallest trees. As agricultural expansion and selective logging razed its home forests in Central and South America, and persecution by humans followed in its wake, the species was among the hardest hit and the first to disappear.  by the International Union for Conservation of Nature, the raptor has already lost around  of its historic habitat and is locally extinct across much of its former distribution.

In Bolivia, one of the few South American countries still lacking a census of the species, the Harpy Eagle’s status remains unknown. “We believe their population has declined, but without an estimate, we don’t know how many are left,” says Kathia Rivero, curator of zoology at the Noel Kempff Mercado Museum of Natural History. 

It was logging of the giant kapok trees that cradled their nests that led to the 2018 rescue in Bolivia of two unrelated Harpy Eagle chicks just a month apart. Roque and Luna, as the male and female nestlings were named, were brought to a wildlife rescue center in the city of Santa Cruz de la Sierra and slowly nursed back to health.

The center’s chief biologist, Raul Rojas, had spoken of returning the birds to the wild—a challenging and costly endeavor that had been achieved with rescued Harpy Eagles elsewhere in South America but never attempted in Bolivia. However, the project stalled in 2020 when Rojas died of COVID-19 during the pandemic. As time slipped away and the eaglets grew, critical survival skills went undeveloped and their habituation to human contact increased. The narrow window for rehabilitation was rapidly closing. “A lot of people thought it was a lost cause, and there are never any guarantees with rehabilitating wildlife,” Rivero says. “But some of us still thought it was worth a try.”

Rivero consulted with raptor rehabilitation specialists and assembled a team of collaborators, funders, and volunteers. Among the latter group was Tavera, who had previously worked on a conservation program for the endangered Andean cat. “I’d never worked with birds before, but the situation with the eagles broke my heart, so I signed up straight away,” she says.

In 2021 the eagles were transferred to Bioparque Curucusí, a zoo outside the city. They were housed in a large flight enclosure secluded within a fragment of rainforest so they could build the muscles and coordination needed for flight in the wild and acclimatize to their natural habitat. Tavera and her colleagues went to extraordinary lengths to reduce Luna and Roque’s habituation to humans, wearing costumes carefully camouflaged to blend with the shadows of the trees whenever they entered the enclosure. Still, readying the raptors for the rainforest would also require priming their predatory instincts by feeding them live prey.

Following strict ethical guidelines, the feeding started with domestic animals such as chickens, ducks, and rabbits. Gradually, wild animals—such as sloths, monkeys, and tegu lizards—were included to familiarize the birds with common quarry. “Even as a biologist, it was challenging to feed them live prey,” Tavera says. “But these are birds of prey, and they could only be ready for release if they could survive in the wild.” By early 2023, the eagles had honed their hunting skills, and release could no longer be delayed. Even so, locating a suitable release site would prove a challenge given the threats facing the eagle in the wild.

The first location considered was the stretch of forest where the eagles had been rescued. In a strange twist, while surveying the area, Tavera encountered the man who felled the tree that brought down one of the nests. “Speaking with him changed my mind. I couldn’t see him as ‘the bad guy,’” she says. “He’d never had an education because of his poverty, so he didn’t understand the damage he had caused or even know what a Harpy Eagle was.”

Nevertheless, logging pressures quickly ruled out that area and several others. A suitable site was eventually discovered in Cinma San Martin, a sustainably managed area of forest in the Bajo Paraguá region of Santa Cruz. The 295,000 acres of rainforest promised an optimal habitat, with minimal threats from humans and plenty of prey.

On the day of their release, the eagles, fitted with radio transmitters, were transported six hours by light aircraft to the release site, where the team waited nervously on the ground. The birds were then transported in boxes to a nearby clearing and set free. Roque, the male, swiftly vanished into the forest while Luna perched on a high branch, watching the humans assembled below before finally soaring out of view. “I felt relief and sadness,” Tavera says. “And then you start to worry about the chances of them surviving.” 

Despite those fears, the eagles haven’t just survived; they are thriving. The pair separated shortly after release, dashing the team’s hopes that they would become a breeding pair. Since September, however, transmitter data show that they have been exploring the area to establish territories of their own. The pace of their activity also indicates that they’ve been acquiring enough energy by hunting. In December, after three months of careful observation, the team officially declared the reintroduction a success.

The accomplishment has fueled optimism of achieving the same result with several other Harpy Eagles languishing in rescue centers in the country. “With Luna and Roque, we’ve gained the hands-on practical experience and skills needed to put more of these birds back in the wild,” Tavera says. Preparing them for release may have been her first time working with birds, but it won’t be her last: Tavera will soon lead the rehabilitation component of a new national conservation program for Harpy Eagles spurred in part by the success with Luna and Roque. She couldn’t be happier to don the ghillie suit once again.