Four more California condors flew to Boise's World Center for Birds of Prey by jet and four more are expected, placing one-quarter of the world's population in Idaho.
And another four condors were due Thursday, bringing the total at the center to 20.Biologists are trying to breed the 20-pound black vultures there. No chicks will be produced until next year at the earliest, said Jeff Cilek, program director for the Peregrine Fund, which runs the center.
All the birds are 2 to 6 years old and they do not breed until age 6, he said.
The center got its first group of 12 in September 1993. The oldest were 5 years old during last spring's breeding season.
Only three California condors are in the wild, at Los Padres National Forest in California. There are 88 in the world.
The others are at two breeding facilities: the San Diego Wild Animal Park, which supplied the quartet on Wednesday, and the Los Angeles Zoo, which is providing Thursday's shipment.
Keeping some of the birds in Idaho has alleviated the overcrowding problems at the other two facilities and protects the genetic diversity of the species, said Michael Spear, Pacific region director of the U.S. Fish and Wildlife Service.
Visitors to the center are not allowed to see the condors, whose wing span reaches 10 feet, because of the threat of disturbance.
The Boise center has worked to pull the peregrine falcon and other endangered birds back from the brink of extinction.