Originally Posted by Dave Wooten
one of my work colleagues recently bought a 2nd hand Canon 100-400 L series zoom with the image stabiliser gizmo. This was a big deal for him philosophically as he is, like me, a manual everything kind of guy when it comes to cameras.
However, he is heavily into bat research and caring for injured wildlife, bats and birds in particular. I must say that the shots he has shown me are outstanding. And he uses Leica for everything else except the flying birds pics so he has high image standards to compare against. He runs the lens on an EOS 3 body to get the super-duper auto focus stuff.
His comment? "I simply could not (reliably) get anything like these shots of flying bats with manual focus lenses."
Hope this helps.
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.