First of all, what a look on Zuni's face in the first shot! Wouldn't want to be that ball.
Second, I can see what you mean. The OOF areas get a bit distorted even with fast shutter speeds. I guess that is what's "off" in my kingfisher shot - even though it's hard to imagine that 1/2000s doesn't freeze everything. Makes sense: with a much larger bird, the camera doesn't pan nearly as fast. Thanks.