I think it is strange that this island in the middle of no where would have bird migration but whatever birds gonna do what a birds gonna do. Supposedly on Easter Island since ancient times, they celebrated the birds arrival and would choose a person known as tangata manu (birdman) to be human representation of the creator god MakeMake. OK I am not going to lie I LOVE that name for the creator God. I am not sure if it is pronounced Makie Makie but that is how I think it should be. :)
I think it is interesting that here is another example of a God represented as a human with a bird head. There are so many examples of this all over the world. The first that comes to mind is Egypt but there are lots of Indian and Native American tribes with a bird man. I am not sure if there was one tribe that went all over the world and that is why you have the same story or if they all communicated with one another or if there was a bird man that went all over and had a different name at each location. I kinda like the idea of a creator god that made five tribes of different colors at the north pole or Mt. Meru and they spread across the world. They would have had the same knowledge and would have gone to their new homes and built pyramids to mirror the mountain they came from.