thanks  Radio-Parrot for the name!
If you really want to make one you can ask :3
http://www.furaffinity.net/view/17494629/ an example of one

Common: Can go with anything
Uncommon: Uncommon x uncommon or uncommon x common (unless stated otherwise)
Rare: rare x common (unless stated otherwise)
very rare: Rarely ever happens. Only available in premade adopts for now (unless full customization is available)

** Note: They aren't birds uwu