Ducks can fly in and out of the Cincinnati zoo. They are attracted to a large pond within the zoo. Here is a hooded merganser (drake) photographed with a Canon 1DX Mark II and the new Canon 600mm f/4 lens with the 1.4x converter - both version III. Having only recently getting both the 600mm and the 1.4x, I had to try it out and the best way is to go to a spot that allowed me to shoot 4,000 images in a couple of hours. I mounted the lens to a Wimberley gimbal head, AF microadjusted the 600mm to only -1, and to +5 when the 1.4x is used for precise autofocus. Focus is AI continuous and exposure is manual. This is an awesome combination for wildlife photography - Canon 1DX Mark II, 600mm, and 1.4x. The 1.4x makes the lens effectively an 840mm f/5.6. It is awesome!