Many other pet bird owners are confused about how to sex their Cockatiels. This information is offered for those of us who, as new bird owners, are still struggling with things that more experienced bird owners take for granted.
Females have mainly grey faces with only traces of yellow around the beak, eyes, and forehead. Their cheek patches appear duller since there is a wash of grey over the orange and their crests are grey. They have yellow spots on the underside of their flight feathers and conspicuous yellow and grey barring on their tails. After their first molt at 6 to 8 months males lack the tail barring and the flight feather spots but have a bright yellow face and "bib." Their crests are mainly yellow with grey only at the tip. The cheek patches are a bright orange since there is no grey there to dull them. The white wing patch is immaterial when sexing.
Normal Whiteface, Cinnamon, Fallow, Silver, Yellowcheek, Pastelface, and any other mutation which results in a basically grey or brown bird with white or yellow accents can be sexed in the same way as the greys. That is females will have grey or brown faces, spots under their flight feathers, and barring on their tails and generally have lighter cheek patches. Males will lack the spots and bars but have white or yellow faces and crests.
Some sources confidently state that male pearls always lose their pearl markings during their juvenile molt but I've recently read that some breeders have developed male pearl birds who do not lose their markings at adulthood or who lose them slowly over a period of years. In any case, after their first molt males will have yellow or white faces and females will have grey or brown ones. The yellow face is probably your best guide at this point.
These birds have no grey at all on them, their bodies cannot make the grey or brown pigments. A bird with a lot of yellow that has dark eyes and perhaps a small area of grey somewhere, even only one feather or toenail, is not a lutino but a pied. Lutinos can be visually sexed since the females will have the same bright yellow spots under the flight feathers and their tails will show a yellow on cream or cream on yellow barring pattern. Males are sexed by the absence of these traits. One note — a very pale lutino may not show the patterns clearly, try holding a shed tail feather up to a strong light. It has been said that Lutino-pearls are difficult to sex. These same people claim some males retain their pearls for several molts and, depending on the extent of the pearling the underwing spots and tail bars may or may not have been present to begin with in either male or female. If you have a baby lutino-pearl with spots and/or bars who loses them in the juvenile molt you know that you've got a male. If you've got an adult without these markings you can be fairly certain it is a male.
Lutino Whitefaces (a.k.a. Albinos) can't be visually sexed. An alternative method such as blood sexing, feather sexing, or surgical sexing may be necessary. Sexing by feeling the pelvic bones is generally held to be unreliable and potentially dangerous if done by an inexperienced person. Sexing in this manner generally is not accurate anyway until the bird reaches maturity and in the case of a female, has laid eggs previously. If your pied Cockatiel has some dark tail feathers, it may be possible to tell by the barring or lack of barring on the tail feathers.
• If a bird lays an egg it's a female.
• Some mutations are sex-linked and you can often tell the sex of these by knowing the colors of the parents. Lutinos, Cinnamons, and Pearls are common sex linked mutations. Basically, if the father carries the sex-linked color either visually or as a split and the mother does not visually show that color, (females can't be split to a sex link mutation — yes, this is backwards from humans and other mammals) any babies with that coloring are female. When the male parent is split not all of the female babies will be the mutation color but all babies of the mutation color will be female.
• In general males whistle and females are quieter but there are exceptions.
• Two birds of the same sex who both have strong parental instincts may form a pair bond and go through the motions of mating and nesting. A friend of mine had two female lutinos set up together and producing large numbers of infertile eggs before she was told about the spots and bars.
• Unless you want to breed your birds it is not really necessary to know what sex they are but knowing may make it easier to choose an appropriate name and add to your general enjoyment of your pet.