Joe Fortin Thank you for the compliment and even more so for the question.
I don't actually track the birds when shooting the birds. Just to the left of the image is a bird feeder. I know that the birds (the Grosbeaks in particular) normally come in from the right and sorta hover just next to the feeder.
The camera is actually set up on a tripod with a remote. This way I can see a wider field of view and anticipate when the bird will be the camera's sights.
Richard Morwood I'm always impressed by your bird photography! How do you track the birds at 600mm???