However, as with conventional photography, a judicious combination of automatic and manual control will yield more consistent results. There are two strategies here. For automatic focusing, focus the scope on the subject, and then allow the camera to autofocus through the scope. Using the camera for autofocus is helpful when it's hard to clearly see the camera's preview screen. However, the camera's autofocus process inserts a substantial delay, up to about a second, between pressing the shutter and firing as the lens racks in and out.
Birds seem to sense what's happening, and enjoy moving significantly during that delay.
Use the camera's focus confirmation to help determine best focus. If your scope support is adequate, the field of view won't change or vibrate while you focus. What can happen while the camera focuses The great advantage of this technique is that since the camera focus is fixed, there is no delay between depressing the shutter button and firing. It also gives you unambiguous control over the point of focus, even with an obstructed view. The focus point for the camera will be slightly different than that for your eye, so you'll need to tweak the scope focus for the camera.