It does look like a Bird but it too is natural. Trying Googling Indian Effigies and look at the pictures. If they wanted to make something to look like an animal they were very good at making it look exactly like one.
Check out these images and you will see what I mean.
Try to stay away from what it looks like. If they carved it to look like a bird it would. Almost all of the rocks you find can look like something if you look at it hard enough. I think most went through that stage when we 1st started hunting, I know I did