Controlling where a spotting scope, telescope, or high-powered binocular is pointing can be a tricky task. But by using the Piggyback 1/4"-20 Slow Motion Controls from Vixen between your lens/spotting scope/binocular and your tripod head, you'll gain accurate slow motion adjustment in both elevation and azimuth axes (up/down & left/right).
The device has a standard 1/4"-20 threaded tripod screw upon the bottom, and thus attaches to anything with a 1/4"-20 threaded tripod screw. On top it has a standard 1/4"-20 threaded tripod screw so that you can put any lightweight spotting scope, telescope, or binocular upon it.
Being quite stable and not terribly heavy, it is a popular accessory to put between a spotting scope and the fluid head moving it about to achieve the ultimate in control. You'll have the capacity to follow birds in flight at moderate magnification with the fluid head itself, as well as zeroing in upon stationary birds at high magnification with the Piggyback unit.