Why is the Easter Bunny Australian in Rise of the Guardians?

Why is the Easter Bunny Australian in Rise of the Guardians?

Bunnymund is a Pooka, a philosophical warrior rabbit, and used to live in a village with other Pookas on his homeworld before they were wiped out, leaving him as the only survivor. He currently lives on Earth in his Warren, an oasis deep under the surface of Australia that is said to be the birthplace of spring.