Gliding

I had to run an errand at the local shopping centre this morning, just next to my EB pond. I took the opportunity to test my 120-400 on the new camera. Just when I arrived, this big bird was circling above the pond. This was certainly more interesting that the swimming ducks and geese, but I did not have time to get ready for the shot. Well, I have to admit that I really don't know what "getting ready" for this type of shot means. Neither do I know what kind of bird this is.

Any help to marginally reduce my level of ignorance would be highly appreciated!