Levina, I'd say it does alright but not spectacularly. I think it's no surprise to say that the 7DII does better. However, I'm not shooting a premium white Canon telephoto but my Tamron 150-600. I sold my Canon 400 f/5.6L before I got the 80D; I wish I could test it with that. Maybe I'll test it with my 70-200 2.8 II some day (but that's not really a birding lens).
I was kinda hoping you would respond, Gabe. Even though we talked about it before. 
I started out with a 40D and birds in flight went pretty well so I was thinking the 80D is the latest camera in that line and should do better even. It could very well be that your Tamron is slowing you down some. I shoot BIF with the 400/5.6 and that's still one of the best BIF lenses around and that should make a real difference.
On the other hand, when I was shooting with the 40D I couldn't compare it with anything else, but I've been shooting with 1D bodies for the last 4 years, so switching back to a XXD body may feel like too much of a downgrade especially in the AF department.
Thing is I bought a 1D4 and I like the files and the AF is superb, best ever. But this copy is old, high shutter count, pretty worn, missing covers on the side, it stinks after after shave (really, male photographers have got to stop using after shave!) and it has an incredibly dirty sensor. The whole camera is dirty really. And I'm getting tired of getting these old, worn copies from the shop. Of course, the price tag is accordingly, but for that same money I can buy a new camera, like the 80D or the 7DII.
Anyway, thanks very much, Gabe.
