Call it the first day of the condor. Egged on by recorded king vulture screeches, the first California condor hatched in captivity emerged from its shell - bald head first - at the San Diego Zoo. The rare chick, weighing about half a pound, immediately moved to increase that statistic. ''He just chowed down, he was so hungry,'' a zoo spokesman said. Only 17 California condors are known to exist in the wild.