Dogs-
Protects your livestock outside. There is a big dog, a medium (basic
dog from other HM games, and a small dog. I think the purpose of the
size is by level of experience.
Cats-
Brings you various seeds(depending on which cat you chose). Black,
brown, or white cat.
Bird-
Brings you seeds(Mostly flowers and herbs, and no it won't fly away).
Pig-
Brings you money(Various amounts I think)