Peter Sharpe led his field crew across the narrow spine of Montañon Ridge, a rugged trail on the southeastern side of Santa Cruz Island.
They traversed down loose gravel slopes, dodging the prickly pear cacti that carpet this mountainous terrain. Thin veils of clouds swept over jagged granite boulders and fields of foxtail grasses whipped back and forth. In this undisturbed landscape, there were no other humans in sight.
Sharpe and his team were headed to a remote bald eagle nest where he would band the wings of an eight-week-old chick. As a research ecologist at the Institute for Wildlife Studies, Sharpe directs the bald eagle monitoring program within the Channel Islands National Park, and much of his fieldwork includes visiting hard to reach nests. “Sometimes they may be on a 500ft cliff,” he said.
Located 20 miles off the coast of southern California, the national park encompasses a cluster of five islands, including Santa Cruz, the largest at 96,000 square miles. Each island features a diverse topography of beaches, forests and canyons that house a rich biodiversity of endemic plant and animal species, earning it the nickname “The Galapagos of the West”. It’s one of the least visited national parks in California, but the light visitation allows wildlife to flourish. “A lot of the young birds on the mainland are hit by cars, electrocuted on power lines,” Sharpe said. “On the islands, they’re pretty well protected from manmade threats.”
On his first expedition of banding season, Sharpe was a bit nervous. “I don’t wanna be up a tree with 30mph winds,” he said with a laugh. And it’s not just his own safety he was concerned about. Nestlings cannot fly. If they flare their wings, they could tumble off their perch and end up with a cracked beak, or worse, a broken wing. “It’s a balancing act between not scaring the chicks too much and not stressing the adults too much.”
About 50% of the birds Sharpe bands won’t make it past their first year, but by banding, he’s able to track the bird’s movement in its first few years and know which ones survive.
First day jitters aside, Sharpe was prepared. He joined the Institute for Wildlife Studies in 1997, when the eagle’s population hit its lowest point with only three breeding pairs. Up until the 1950s, bald eagles historically inhabited the islands, but when chemical companies began dumping the toxic pesticide DDT (banned in 1972 by the United States Environmental Protection Agency) into the ocean through the Los Angeles sewer system, the birds all but disappeared. Thinning eggshells, which were linked to contamination in the bird’s food chain, caused most eggs to crack before they hatched. With no chicks to replace adults, their numbers dwindled.
So Sharpe took matters into his own hands. “The extremes we had to go to save the eagles,” he remembered. “I didn’t know anything about this when I applied for the job.” What he thought was a nine-month, temporary contract slowly evolved into a two-decade-long career. “This position, I sort of lucked in to,” he said.
Prior to coming to the islands, Sharpe’s fieldwork included restoring ruffed grouse populations in southern Illinois and surveying the behaviours and habitats of ground squirrels in Idaho. But working with the bald eagles required him to obtain a whole new set of skills – even if that meant challenging his fear of heights.
In a series of rescues akin to something out of a Mission Impossible film, Sharpe dangled from a rope 100ft below a helicopter as it flew to the hardest to reach nests. “The first 10 times, I was focused on not dying,” he recalled. “I just learned, enjoy the view; not many people are going to see the island from this angle.” Hovering over 1,500ft cliffs, Sharpe retrieved the fragile eggs, which were transported to the San Francisco Zoo for the remainder of their incubation period.
Since those rescues ended in 2006, 129 chicks have hatched naturally on the islands. Today, the eagle population includes 20 breeding pairs, and this season, he’s monitoring the progress of 13 chicks (with the possibility of 14) across all five of the islands.
After hiking for two hours, Sharpe spotted the chick on top of a dried out Ironwood tree. Two adult eagles circled overhead, squawking at his intrusion. He unpacked a bag of supplies: pliers and callipers for the wing markers; needles, syringes and vials for the blood draw. Then he stepped into a climbing harness, carabineers clanging at his waste and straps on his safety helmet.
“Hi there,” he said to the bird, speaking softly, as if it was his child. In a matter of minutes, he lowered the bird to the ground in a duffle bag and his real work began.
First he measured the beak depth and leg size, which reveals the sex: females will grow 25% larger than males. Then he drew blood and placed a patagial marker on its left wing. With a letter and number identification code, this ID tag helps biologists identify the birds once they leave the nest. He had all the calmness and precision of an ER surgeon – not one moment went to waste.
Determined to bring our national bird back to its historical habitat, Sharpe placed the chick back into the centre of its nest and let out a sigh. “One down, who knows how many to go.”
If you liked this story, sign up for the weekly bbc.com features newsletter, called “If You Only Read 6 Things This Week”. A handpicked selection of stories from BBC Future, Earth, Culture, Capital, Travel and Autos, delivered to your inbox every Friday.