That is a fantastic photo. The 600mm must be a lot of fun not to mention the results on the 1D Mark II. How far away were you? At f4.5 you had to be pretty close. I'm guessing 50 meters.
This looks like the same family of birds I shot today on a small lake outside Ho Chi Minh City.http://www.pbase.com/smacomber/image/91554365/original Do you think this bird in my area is the same as the bird you photo'd?
Thanks for sharing the photo.