Especially if we talk about pigeons , because pigeons are different in many ways from mammals. Even more interesting, at least from the bird's point of view, is that male pigeons have two XX chromosomes and females only one.
Females also carry a little slug of material in addition to their X chromosome.
That little slug of material can be passed on to an egg, but for most purposes we can ignore it because it seems to carry very little information of interest to us. All chromosomes, including these X chromosomes, carry information on them which the bird's body uses like the commands of a computer program. Some of this information is stuff that we as breeders want, and some is stuff which we don't. The stuff we want might include instructions to grow feathers which curl on the wing shield, or to produce pearl eyes instead of orange ones. Some stuff we don't want might include instructions to grow extra toes or crest or webs on the feet.