The Wimberley SK-100 Sidekick quickly converts any ballhead with an Arca-style quick release clamp into a gimbal head. This allows the lens to rotate around its center of gravity, dramatically improving handling and vibration dampening. Your percentage of 'keeper' shots will definitely go up using this device with telephotos with a tripod collar.
Ideal for 300mm f/2.8 or 500mm f/4.5 lenses, but also works great with 70-200/f 2.8 telephoto zooms or macro lenses with tripod collars such as the 180mm f/3.5 & 400mm f/5.6's made today. When the tripod collar is fitted in the Sidekick properly, you will have perfect 50/50 weight distribution, making movement of the lens and camera finger-light.
The Sidekick, when combined with an appropriate ballhead with an Arca-type quick release clamp & independent panning lock as well as an appropriate quick release plate, makes for an incredible combination to provide control of spotting scopes. This is likely the best possible scenario for tracking a bird in flight, but will require a spotting scope with a rotating tripod collar in order to be ergonomically practical. (See Wimberley Website for complete details)