California condors can be born from "virgin births" in what is believed to be the first case of its kind, a new study has found.
Researchers from the San Diego Zoo Wildlife Alliance said they believe it is the first time any female bird has given birth without her eggs being fertilised by a male while still having access to a male bird.
This is also the first report of asexual reproduction in California condors.
Oliver Ryder, the study’s co-author and director of conservation genetics for the San Diego Zoo Wildlife Alliance, said the findings could mean that asexual reproduction could occur in other species.
Two male chicks were hatched from unfertilised eggs. They were only related to their mothers, and neither of the chicks was related to a male.
Researchers carried out genetic testing on the chicks. The study was published in the Journal of Heredity - a scientific journal that deals with genetics.
Reproduction without fertilisation from an egg - also known as parthenogenesis - can also occur in other animals including: sharks, honey bees, and Komodo dragons.
In birds, it usually only occurs when females don't have access to males.
Each mother condor in the study had previously bred with male condors, producing 34 chicks in total.
But all the mother condors studied in the research were housed with a male when they produced eggs through parthenogenesis.
San Diego Zoo and Safari Park, who conducted the study, has been involved in a California condor breeding programme that helped bring the giant vultures back from the brink of extinction.
California condors are the largest flying birds in North America, and have wing-spans of over three metres.
They were once common across the west coast of the USA, but only 22 survived when the US government captured them and placed in breeding programmes in the 1980s.
Now there are more than 500 California condors. 300 of these birds have been released into the wild across the US.