I came across a very friendly belted king fisher today. He was flying between two perches. Incidentally I had a 7D2 on me (fresh body recently purchased). I was able to grab a few frames with the 400 DO II. Below is one of the frames. I hope you like it. Unlike the 1DX, the AF does slow down with the 2X III, a bit too slow for catching a king fisher in flight, so I changed to the 1.4X III for max. AF speed. I still wish I had my 1DX, there is simply no contest but the 7D2 sure is good value for $1500! IMO the old one while it was great for perched birds wasn't good for this kind of flight shots at all but the new one has some real improvement. Any ways, I hope you like this frame
7D2 400 DO II + 1.4X III. ISO 1000. f/5.6 at 1/2500sec hand held. Processed with DPP 4.3. (Really wished to shoot at ISO 1600 to gain a bit more ss but from earlier frames it would get too noisy for my liking)