There are in fact many things in common between shooting athletes and shooting birds:
This is an over-simplification. There are many ways to photograph either athletes or wildlife. Action photos have similarities but there's more to athletes and wildlife (birds in particular) than action.
What hasselbladfan hasn't mentioned is whether he wants to stay comfortably inside the box or if he wants to make unique photos. Nick Brandt's african wildlife photos comes to mind: http://www.nickbrandt.com/
He's using equipment that is so far outside the box that it's never been on anyone else's radar screen... and his photos are uniquely fabulous.