Dave,
Concerning the lens for birds, Arthur Morris (a well-known bird photographer in the USA) at one time favored using the Canon 400/5.6L as a handheld lens for birds in flight. I have this lens and like it but I'm not a birding specialist. It also does extremely well with the Canon 1.4x extender, making a sharp manual focus 560mm f/8.
If I remember correctly, I saw a video showing Roger Tory Peterson using a handheld Nikon with a 400mm lens back in the manual focus days.