A California condor spreads its wings on a rock

The California condors are a Critically Endangered species of vulture that lives on America's western coastline. Image © Shutterstock / Barbara Ash

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California condors can have chicks through 'virgin births'

One of the world's most endangered birds can have young without mating, it has been found.

Researchers studying the California condor discovered two chicks with no father in a shock finding that may affect how the species is conserved.

A critically endangered vulture is capable of 'virgin births', even when birds of both sexes are present.

Scientists investigating the genetics of the California condor found two chicks were unrelated to any potential father even though their mothers had been housed with males. 

This process, known as parthenogenesis, is relatively rare in birds but is more common in other parts of the animal kingdom, such as in reptiles.

Dr Oliver Ryder, the study's lead author, says, 'This is truly an amazing discovery. We were not exactly looking for evidence of parthenogenesis, it just hit us in the face.

'Our results showed that both eggs possessed the expected male sex chromosomes, but all markers were only inherited from their dams.'

The study, led by researchers from San Diego Zoo, was published in the Journal of Heredity.

A California condor sticks its head into another's face

The California condors are now part of a breeding programme to save the species, with some living wild and others in captivity. Image © Shutterstock / MTKhaled mahmud

Who's the daddy?

California condors are a species of vulture once found across the western coast of the USA. It soars over scrubland and forests looking for carcasses of dead mammals it can scavenge from.

Since the arrival of humans in the Americas tens of thousands of years ago, the population of the condor has been in decline. This has been attributed to the extinction of large mammals in the Americas, such as mammoths, dire wolves and ground sloths.

Without these large animals to scavenge from, condor numbers fell. It is thought that the bird's current restriction to the west coast is due to it switching to scavenge from the washed-up carcasses of marine mammals.

The arrival of Europeans in the Americas in the past few hundred years has caused their population to fall still further. As well as persecuting the birds, hunters use lead shot, which poisons many of the carcasses scavenged by the condor. This has accelerated their population decline.

By 1981, there were just 22 California condors left in the world. Shortly afterwards, the remaining birds were taken into captivity as part of a breeding programme to conserve the species. There are now hundreds of condors, with signs the species may be classified as Endangered in the near future.

However, the population bottleneck means that the species suffers from inbreeding depression, where rare, often negative, traits become fixed in the population. In the case of the condors, they suffer from a condition known as chondrodystrophy, which affects their skeletal development.

The breeding programme attempts to counter these effects by deciphering the genetics of each condor. This allows conservationists to work out which birds are best bred with each other to keep the population healthy.

While studying samples from across the history of the programme, researchers found two young males with unusual genetics. While they shared the genetics of their mothers, they didn't share any of the genes of the males presumed to be their parents.

In fact, they didn't share genes with any known male California condor at all.

A white turkey

Turkeys are known to have parthenote offspring, but only when they are kept isolated from males. Image © Shutterstock / mmpixel91

The parthenote problem

Digging deeper into the mystery, researchers found that the genes of the father would have to be identical to their mothers, suggesting strongly that the chicks were the product of parthenogenesis.

This process sees unfertilised eggs develop into an embryo, something that isn't normally possible as unfertilised eggs contain only half the DNA needed to build an organism. The other half is normally provided in the sperm of the male.

In parthenogenesis, however, the egg divides differently to how it would normally, leaving it with a full set of genes from just the mother. Alternatively, the division can happen as normal, but the products fuse back together to complete the genome.

Some other species, such as turkeys, are capable of the process, but only when females are kept apart from males. In the California condor, the mothers were both kept with a mate who they had many chicks with over the years.

Dr Cynthia Steiner, a co-author on the study, says, 'We believe that our findings represent the first instance of facultative avian parthenogenesis in a wild bird species, where both a male and a female are housed together. 

'Unlike other examples of avian parthenogenesis, these two occurrences are not explained by the absence of a suitable male.'

The researchers are now trying to understand what implications parthenogenesis in the condor will have. While it will likely affect which birds are bred together, there may also be health implications.

Both chicks born via parthenogenesis both died at a relatively young age for the species, which can live for up to 60 years. One died at just under two years old after 'poor integration with wild birds', while the other kept in captivity showed abnormal behaviour and development.

As neither of these condors had offspring, researchers are unsure if being born by parthenogenesis predisposes them to developmental issues as has been suggested in some snakes. The scientists also want to find out whether the process may just be limited to birds in the breeding programme, or whether it is common among wild birds.

In either case, parthenogenesis will not save the California condor. With only two virgin births in more than 37 years of the breeding programme, work continues to save the species the old-fashioned way.