In early March last year, an endangered California condor – one of fewer than 350 of its species left in the wild – sat on a cliff in Arizona and stared into space for days. It’s probably sick from lead poisoning, thought Tim Hauck, director of the condor program at the Peregrine Fund, a nonprofit conservation group that helps reintroduce condors to the skies above the Grand Canyon and Zion. These bald-headed scavengers — weighing up to 25 pounds and sporting black-feathered wings that span nearly 10 feet — often fall victim to lead exposure when they consume the meat of cows, coyotes and other large mammals brought in by ranchers and hunters Killed by lead bullets. Listlessness and slouching posture are telltale signs. “We thought, I bet this bird got into something bad,” Hauck said.

His team of eight wildlife biologists stationed at Arizona’s scenic Vermillion Cliffs National Monument, 150 miles north of Flagstaff, hoped the sick condor would slide down from its 1,000-foot sandstone ledge to visit their feeding station, where they would catch it and could heal investigation. The Peregrine Fund provides supplemental food to the condors, most of which have been raised in captivity and released into the wild, to help biologists easily catch them for regular examinations, provide treatment for lead poisoning, protect them against West Nile disease, and, among other things, Vaccinate the virus and keep up-to-date equipment to track the whereabouts of the condors.

When the sick bird was finally caught at the feeding station a week later, Hauck immediately noticed something he had never seen in lead-poisoned condors. His eyes were cloudy, a condition called corneal edema. He consulted with Stephanie Lamb, a veterinarian who volunteers at the Liberty Wildlife Center, a partner organization of the Peregrine Fund in Phoenix. He wanted to know if she thought the condor might be sick with something more worrisome than lead poisoning: highly pathogenic avian influenza, or HPAI, the virus responsible for the deaths of millions of wild birds and domestic chickens worldwide over the past two years. HPAI kills 90 to 100 percent of infected domestic poultry, often within 48 hours, although less is known about mortality rates in wild birds. Corneal edema, Lamb told him, was actually on the list of symptoms.

Hauck’s team took the condor four and a half hours south to the Liberty Wildlife Center’s quarantine facility, where it received emergency treatment and testing. Then, while they were still waiting for the results, the situation at Vermillion Cliffs got worse: a dead condor was spotted near a cave where it was nesting. The team retrieved the carcass and immediately sent it to the US Fish and Wildlife Service Forensics Laboratory in Ashland, Oregon, with an urgent request for an expedited autopsy. Aware of the grave threat an avian flu outbreak posed to the critically endangered California condor, the lab soon confirmed fears that the condor had succumbed to avian flu.

A wave of panic overwhelmed Hauck and his crew. Condors are social creatures. They sleep in groups and gather in hungry hordes to devour rotting animal carcasses, spread saliva and poop everywhere. Hauck describes it as a “feeding frenzy” – ideal conditions for the disease to spread. Additionally, the virus thrives in damp, cold conditions; It was a wet spring, and condors nest in burrows that tend to be moist and cooler than the outside air. Hauck feared that the disease, which is transmitted through the air and body fluids, would spread through the condor population “like wildfire.” He knew they had to contain it.

Since the feeding station was already closed to prevent the birds from gathering, the biologists put on protective clothing. Their goal was to recover the dead to prevent them from infecting other scavengers and to save any sick condors they could capture for treatment at the Liberty Wildlife Center.

They worked 14 hour days, climbing cliffs, rappelling down canyons and roaming the banks of the Colorado River by boat, retrieving dead condors almost daily. It felt like a nightmare that would never end, said Hauck. “It was a three-week period during which we lost 21 birds.” Every carcass recovered tested positive for HPAI.

In less than a month, nearly 20 percent of southwestern California’s condor population had disappeared into Arizona and Utah. Conservationists feared the virus would next affect condors in California. Then, as quickly as the virus flared up, it fizzled out. With the end of the spring migration season and the return of hot, sunny days, condor deaths in Arizona stopped and condors in California were spared.

The U.S. Fish and Wildlife Service recognized that the outbreak could have been much worse – wiping out dozens more condors in several states and possibly even killing animals in the zoo’s breeding herd – and appealed to the U.S. Department of Agriculture Authorize the emergency use of an avian influenza vaccine to vaccinate condors in the event of another outbreak.

It was a vision. While vaccines against HPAI are used in some other countries, for reasons ranging from practical to political, U.S. health authorities have never approved vaccination for any animal in the country – not even poultry. But faced with a deadly threat to one of the country’s most endangered species, condor advocates hoped they could persuade the USDA to make an unprecedented exception.