double yellow

Question
how can you tell if the bird is male or female

Answer
There really is no way to tell unless you get the bird DNA or surgically sexed. Unless you're using the bird for breeding purposes, this is not necessary information, but if you really want to know, your vet can sex the bird for you. If you do plan on breeding the bird, visit your vet first to make sure the bird is healthy enough to breed, and has no genetic defects that would be passed on to the babies.