I have bred a grey cockatiel with a pearl (yellow) cockatiel and and need help sexing the babies... they are already more than 6 months old (around 7 months)
Well, it would help if you told us what they look like.
Males whistle more, and in greys have a yellow face and crest. Usually in pearls, I have found that the females still have their spots after about two or three years, and the males lose them.
If you can't tell by the physical markings of cockatiels then you can go by their behaviour.
Males will be more whistly and trying to get your attention by "bowing" a little and spreading their wings a bit. Females are quieter and screech rather than whistle.
