Even more rarely do birds reproduce that way. Turkeys, chickens, pigeons and certain kinds of finches have laid eggs without the help of a male, though in most cases, their offspring died before they could fully develop.
Now, scientists at the San Diego Zoo say the California condor — the largest flying bird in North America with a 10-foot wingspan — can be added to the list. In a paper published last week in the Journal of Heredity, the scientists said parthenogenesis has been observed in condors for the first time.
“This finding raises the question about whether parthenogenesis is going on more often with birds than we had previously realized,” Oliver Ryder, a co-author of the study and the director of conservation genetics at the San Diego Zoo Wildlife Alliance, told The Washington Post.
A relic of the late Pleistocene era, when saber-toothed cats and woolly mammoths roamed North America, the California condor can fly up to 15,000 feet above the ground and glide for long distances without flapping their wings. They often feed on the carcasses of animals like pigs, cattle and even sea creatures like whales, according to the Cornell Lab.
But survival has not been easy. In 1982, their population dipped to just 22, thanks primarily to the prevalence of hunting with lead ammunition, which poisons the dead animals that condors eat. Condors have also died after flying into power lines and consuming human products, like antifreeze.
Efforts to restore the condor population began in the ‘80s. The birds were taken into managed care, and a breeding program began. In an effort to prevent the breeding of close relatives and identify the sexes of the birds, Ryder and his colleagues took DNA fingerprints of the birds. As the population grew over the years, so did a database of all the genetic profiles of the condors that were born in a facility — as well as those found in the wild, Ryder explained.
As of 2020, the California condor population hovered just above 500, according to the U.S. Fish and Wildlife Service, and the birds remain protected under the Endangered Species Act.
While examining the database that contained genetic profiles of every condor born since the restoration effort, Ryder and his colleagues noticed something strange and unexpected: Two of the condors were biologically fatherless. Born to two different mothers in captivity years apart, the chicks only carried their mothers’ genes, and no genes matching any of the male birds in the database, Ryder said.
“We established there was no male that could be the father to these chicks,” Ryder said. “The chicks were also genetically uniform in a way that they only had genes from their mother.”
Moreover, the mothers of the fatherless chicks had been regularly housed in facilities with fertile male condors, making them the first known instance of birds parthenogenically reproducing when they had access to a mate, according to the study. And to be clear, Ryder said, the births of the two condors were not technically “virgin births.”
First of all, he said, “birth” takes place with mammals, and birds and reptiles “hatch.” Secondly, he said, the mothers of the two chicks had reproduced with males before and were not technically virgins. “They have lots of, I guess you could say, sexual experience,” Ryder said.
Both of the chicks are now dead, according to the study. One died in 2003 at about 2 years old because of “poor integration with wild birds” and “poor food consumption.” In 2017, the other died at 8 of complications from an injured foot, according to the study.
Nevertheless, Ryder said the discovery raised the question of whether parthenogenesis occurred because the condor population had dwindled to such low numbers. But that is just one possibility. At this point, he said, more research needs to take place.
“Nature continues to teach us,” Ryder said. “We think we understand something, and then you make a finding like this and the world looks different after that.”