In 1987, the California condor vanished from the wild, leaving just 27 birds confined to zoos. But the hidden killer was never habitat loss.

The California condor is the largest flying land bird in North America, with a wingspan of about nine and a half feet and a weight of roughly 25 pounds. It can cover 150 miles in a day by riding columns of warm air, sometimes reaching heights of 15,000 feet without flapping. The species has existed for tens of thousands of years, and its role in cleaning carcasses from the landscape made it a vita…