Results from a recent study by US wildlife scientists found that two female California condors gave birth to chicks without any male genetic DNA, BBC reported.

"This is truly an amazing discovery," Oliver Ryder, director of conservation genetics at San Diego Zoo Wildlife Alliance (SDZWA) and a co-author of the study, said in a press release. "We only confirmed it because of the normal genetic studies we do to prove parentage. Our results showed that both eggs possessed the expected male ZZ sex chromosomes, but all markers were only inherited from [female condors], verifying our findings."

Researchers made the discovery during a routine analysis of biological samples, which have been collected from more than 900 condors over the last three decades as part of a collaboration between the zoo and the California Condor Program.

Previously, scientists had only observed the rare phenomenon of "virgin births" in certain species of birds – such as domestic turkeys and chickens – that had been separated from males, according to the Journal of Heredity.

The births marked the first documentation of asexual reproduction in an avian species where the female bird had access to a mate. Both of the female condors were consistently housed with a fertile male and produced several offspring with mates over the years, according to an SDZWA press release.

According to the California Department of Fish and Wildlife, the California condor is a critically endangered species that has recuperated from borderline extinction due to major conservation efforts. Captive-bred California condors have been released throughout the Southwest and Mexico, raising the species' current number to approximately 500.

This article was originally published by Business Insider.