This is an example of how it is virtually impossible to get good (correct subject and sharp)
focus on a distant bird in a confused setting of trees and rushes etc. Even with a faster shutter
and less camera 'shake' it would have still been OOF.

The subject was about 800 yards away. Note that focus was actually on the rushes
just in front of the bird and this could not be seen in the viewfinder.
(Cropped. Monopod used).
I think an AF lens is definitely required if you want to reliably grab something like this.