Yesterday I expressed some concern about tracking capability of EOS R.
https://www.dpreview.com/forums/thread/4328423
With DSLR when you track a bird you see the bird all the time as you keep shooting. You can track the bird or any other moving subject without any problem. With mirrorless when you pan without shooting you see the subject all the time. But when start shooting with mirrorless while trying to track all you see is the shots you have taken one after another similar to a fast slide show. There is a lag between the time you have taken a shot and it comes up in the viewfinder. So, it becomes difficult to know the exact position of the bird at any given time. This is what bothered me yesterday when I tried to shoot few BIF. I went out again today to test it more. I wanted to shoot some local terns which are small and fly very fast. Luckily, I am not that disappointed. It is not as good as DSLR, but much better than my initial impression.
Here is a sequence from today.

I was doing alright with the first 4 shots. At this time although I thought the bird was in the middle of the frame it had actually moved to the margin of the frame. Sequence after sequence this happened. But the good news is that it is possible to shoot very good BIF with EOS. See the larger sizes of the first 4 pictures.




I know, EOS R is not an action camera, but it should be able to track moving subjects if needed, although not as good as DSLRs. With larger subjects (animals, human, car etc), it is much easier.
Few more pictures from today.

Oystercatchers on beach
Local birdhide

I used 100-400 II. The lens felt as good as it is with my 5D IV.