The Tiny Threat That’s Killing North America’s Largest Bird

Some critically endangered California condors carry genes that are causing fatal dwarfism in their offspring. Scientists are working on a genetic test to help save the species.

 

Every egg matters when you’re trying to save a critically endangered bird from extinction.

That’s especially true for California condors, North America’s largest birds with a 10-foot wingspan. Condors nearly went extinct in the 1980s as a result of hunting, lead contamination, DDT poisoning, and other factors. The last 22 California condors were brought into captivity in 1987 in a last-ditch effort to breed them in safety and save the species from disappearing.

That desperate move was a success. Today, the California condor population has risen to more than 435—all descended from just 14 breeding individuals—and the birds have returned to the skies above California, Arizona, Utah, and Baja, Mexico.

That number would be much higher, however, if every California condor egg hatched a healthy young chick. That isn’t always the case. Eggs fail in captivity and in the wild for a number of reasons, but one of the most worrying is a rare genetic condition called chondrodystrophy, a lethal form of dwarfism.

 “The chicks born with this disease show very short extremities,” said Cynthia Steiner, acting associate director of genetics at San Diego Zoo Global, who is studying the disease. “It produces late embryonic mortality. The chicks die right before or right after hatching.”

Chondrodystrophy first showed up in five California condor eggs in the late 1990s, a period when the population was just starting to climb again. “It was a big alarm for the managers of the captive population,” Steiner said. Since then the problem has shown up several other times, although exactly how often is unclear because not every failed egg is fully examined to determine why it did not hatch successfully. Steiner said the data researchers do have suggests that some form of malformation and embryonic death affected about 120 fertile eggs over the past 22 years.

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