I'm pretty sure only one of them is a bird, and they're all unique. I guess theoretically multiple people can summon them if they have the ability, but as for the spirits themselves there's only one of them.

I can definitely try, though most people just get really confused when I try to tell them about it. In any case though, until a few years ago my world was actually two separate worlds. After a certain event though, they combined into one single world.