I was using Auto Area AF with some blocked out distance spots along with animal detection. Bird detection is not supported in AC yet. Hope it will get added.
I had used this with my 100-400 successfully on 4.0 when there was no Bird detection, but was struggling with it on this fountain.
This morning I switched to C1 with a 19x7 rectangle along the top of the fountain. Took 2655 shots and most were in focus. Only Auto Area AF supports blocking out focus spots so I could not do that but it didn't matter.
Bird detection is good in a situations like this I hope it gets added to the FW.