Your bird will go through a molt of its juvenile feathers between 6 and 12 months of age, depending on the species. The breeder who sold you the bird may have had the baby sexed before selling it to you. If so, you should have received a certificate or letter stating the sex. If not, the breeder should be able to help you find out if there are any distinguishing marks to tell males from females in that species. In many birds, there are no external marks or ways to tell gender visually. To sex birds like this, you need to perform some sort of medical test. There are several methods used to determine gender.
Blood sexing requires a couple of drops of blood out of the bird’s toenail, and a laboratory actually looks at the DNA in the blood to determine gender. This method is quite safe and relatively painless.
Feather sexing requires you to pull some feathers, and examine something like a DNA test of the feather tissue to determine the sex of the bird. This method needs a steady hand to pull out those feathers but is almost painless for the bird.
Surgical sexing requires that the bird be put under anesthesia. A small incision is made in the bird’s side, and a scope is inserted into the incision. The veterinarian actually looks at the sex organs through the scope. Results are immediate, but there is always some danger to the bird from the anesthesia, and from post-operative complications.