According to Wikipedia before the first molting the male and female have the same markings as an adult female. Adult cockatiels are sexually dimorphic, though to a lesser degree than many other avian species. This is only evident after the first molting, typically occurring about six to nine months after hatching: The male loses the white or yellow barring and spots on the underside of his tail feathers and wings. The grey feathers on his cheeks and crest are replaced by bright yellow feathers, while the orange cheek patch becomes brighter and more distinct. The face and crest of the female will typically remain mostly grey, though also with an orange cheek patch. Additionally, the female commonly retains the horizontal barring on the underside of her tail feathers.