So, your standard animal: XX for a female, XY for a male, right?
For pigeons (and also other birds, and insects, and reptiles), sex chromosomes are referred to with Zs and Ws. This is because their sex chromosomes are completely different from that of mammals. No genes are shared between them at all. (They're most like our chromosomes 3 and 5).
Not all mammals are XX/XY-- platypi prove mammals evolved sex chromosomes at least twice-- but this is a blog about pigeons so we aren't going to get into the weeds there.
Anyway, at a basic level, you can think of bird sex chromosomes as working "opposite" to what you're used to. ZZ for males, ZW for females. This will be relevant, as color and trait inheritance is impacted by this fact, and if you're used to mammalian inheritance it will trip you up.
