by Sonia Drew, BBC News
The California condor chicks are being cared for by biologists in San Diego
Seven rare California condors have been born at a wildlife sanctuary for an estimated 1,500 of the wild birds.
All the chicks were conceived in artificial incubators at the Nisei Raptor Center in Southern California, and were born without the aid of birth control.
The chicks will be released into the wild when they are old enough.
Known as the proudest birds in the world, condors are protected under the California Condor Protection Act.
The breed is particularly vulnerable to loss because condors are fairly low on the food chain.
Although condors are protected under the California Condor Protection Act, they are still hunted for their meat, feathers and ivory.
Condors are found in Mexico, Colorado, California, Nevada, Utah and parts of Arizona.
One of the birds then became the first California condor to be fitted with a satellite tracking device and released into the wild, more than 15 years ago.
Irina Koria, one of the researchers at the Nisei Raptor Center, explained that however rare the new arrivals may be, they will in due course look after themselves.
“They’re what we call tropical vultures – they fly up to 40,000ft [12,300m] at night and then they graze on grass,” she told the BBC News website.
“They can make up to six flights a day and they’ll probably go back up again very quickly and get down again.
“They have an incredible sense of hearing, and their prey… give off an amazing aroma of things like conchs or coconuts, so when they go after a particular meal they can smell it thousands of miles away.”