In a remote canyon in the Big Sur backcountry, Sayre Flannagan stared at the face of a 300-foot cliff a third of a mile away. As her handheld radio-tracker blipped like a radar detector, Flannagan, a Ventana Wildlife Society (VWS) biologist, had finally located a 10-year-old male condor that she and her colleagues refer to as Number 168.

The VWS’s monitoring equipment had not been picking up a signal from Number 168, which is tagged with a GPS tracking device, for five days. There was a chance that the bird had died, but it could mean that the bird was in a hole somewhere, undetectable to their high-tech tracking equipment. The scientists had started to hope that Number 168 and his female companion, Number 208, might be nesting. That would be a huge milestone—one that VWS has been working towards for years.

Until quite recently, wild California condors were on the brink of extinction. Indiscriminate shooting and lead poisoning had decimated the population by the early 1900s. In 1987, the last wild condor was captured and placed in a captive breeding program with 26 other birds. VWS, a locally based nonprofit organization, has played a big role in that recovery program since 1987.

The program has allowed the population to surge back up to over 270 birds, including 136 that have been released back into the wild. Twenty-eight currently reside in the Big Sur backcountry.

The biologists and volunteers of VWS have been focusing their efforts on creating a self-sustaining wild population. They have looked forward to the day when a pair of their birds would take a crucial step toward this goal by mating and producing an egg.

The VWS program involves lots of backcountry fieldwork. A couple of days before Flannagan spotted the cave, two other VWS biologists had headed into the scrubby, steep terrain of the Ventana Wilderness searching for Number 168. They climbed to the top of the highest peak in the area with their equipment, hoping to pick up a signal, to no avail. When they returned to civilization, Joe Burnett, VWS’s Senior Wildlife Biologist, decided to send Flannagan into the wilderness.

Two days later, Flannagan hiked directly to the location that the last GPS coordinates placed the bird. Though she knew that the condor was near, the chances that she would spot it were slim—condors leave their nests for just a few minutes every three or four days to swap off incubation duties. Still, as she searched the sky Flannagan held out hope.

After an hour and a half, she spotted a condor dive-bombing a sharp-shinned hawk in front of the cliff. It was Number 168.

Later, Flannagan told me that the condor’s unusual behavior indicated that the male might be nesting. “Condors aren’t aggressive like that,” she recalled thinking. “There’s something going on. He’s really protective of that rock face.”

After a minute, the huge vulture landed on a ledge and disappeared into a hole that looked like little more than a chink in the rock wall. At that point, Flannagan grew more hopeful. “A male adult would not be hiding in a hole on a beautiful day unless there was a nest,” she thought.

Flannagan left the area elated. This nest would be proof that the condors are on their way to maintaining their species in the wild. She related the incident to Burnett, who has worked with condors for 11 years. He agreed that the behavior she witnessed indicated that the birds were nesting. Burnett knew he would need to get a biologist into the cave to confirm the presence of an egg.

He also realized that if there was in fact an egg there, VWS biologists would have to get it. The condor that laid the egg, Number 208, was known to have DDE (metabolized DDT poison) in its bloodstream. That can cause the shell to become fragile. He did not want to risk the possibility that the fragile egg would be crushed. VWS would have to remove the live egg and replace it with an epoxy fake. The live egg would then have to be transported to a captive breeding program where the egg would be monitored until it hatched.

The following day, Flannagan led Burnett to the remote location. As soon as he spotted the cliff, Burnett realized that reaching the nest was not going to be easy. The tiny cave sits 100 feet off the ground, with the cliff’s base surrounded by a dense moat of chaparral.

Over the next few weeks, Burnett scrambled to develop a plan to reach the cave. He found a local pilot, Jim Cheatham, to fly a crew to the top of the cliff via helicopter. He also contacted two biologists with years of climbing experience, Joseph Brandt and Scott Scherbinsky, who agreed to join Burnett on the complex mission.

With vertiginous cliffs, a helicopter and a climbing team, the undertaking started to look more like an extreme sporting event than a typical scientific assignment.