The only way to tell for sure whether a parakeet is male or female is to have it DNA tested, states BirdTricks.com. As a rule, however, it is possible to figure out the sex of budgerigar parakeets by checking the color of the ceres, the bulging tissue above the beak.
For the first 8 months, both boy and girl budgies look about the same. By 4 months, the female cere turns white with a small amount of blue, becoming gray-brown at maturity. The male nasal passages develop into a blue-purple color that becomes more intense during mating. It is harder to determine the sex of pastel parakeets.