How do you tell girl and boy pigeons a part?

You cannot tell boy and girl pigeons apart until they grow up. It is not easy even then. You cannot tell by looking, but by feeling, gently, their pubic bones. The females pubic bones are wider in all breeds, however, this varies from breed to breed. They know. Put the bird in a pen next to a bird that is a known gender. Then watch them. If you put a male next to a male, the male may ignore the

new one. If it is a girl, he usually will start making vocal noises and puffing up his chest to show off and claim territory. If he ignores the new one then you haven't gotten an answer yet. But if he starts crowing and puffing up his chest then new one is likely probably a girl. If you get no results put a known girl in the next pen and see if the new one puffs his chest and so forth. Of course this requires you have other pigeons you know the answer for.

A vet or experienced breeder can check by a process called venting. Don't try this at home, you can really hurt the bird.