Love the shots.
Maybe i am missing something - why do all images by you and others have the bird quite large in the frame, almost as if you are standing next to the bird? If not cropped one would need to quite close to the subjects. 600x2x or longer might help but even then they appear to be too large even for the extreme focal lengths.
Would appreciate some insights.
1200mm really does help. The rabbit shot is full frame, here is the finch ( pictured below) strait out of the camera not processed at all. You can see I cropped a little off the left side but very little. I get fairly close for most of my shots. The turkey and the duck above are fulll frame. I actually had to back up on the turkey I was clipping the tail fan. I was at 600mm for that one. The woodpecker is also full frame right above.