Hi Steve.
I'm still experimenting to be honest. I'm not sure bursts work much better than 1 shot, just more pictures to delete
, but worth trying.
So for birds that fly in more of a straight line I tend to try and get them in sight when they are far out, you can normally get an idea \ hope where they are going and then refocus when closer. I find the tracking does not work so after the first focus the next ones are unlikely to be good. I am wondering whether my cheaper Oly 40-150mm, in good light, focuses as well or better than the Panny 100-400mm, or if I just find it easier as its so light and therefore so easy to hold, resulting in better images. Nothing conclusive, just a gut feeling - the last 2 photos are with it and arguably the best. Am wondering whether to move my 100-400 on and go with Canon for BIF or swap it for a 100-300 which would probably do me, or what Mike uses a 40-150+TC.
I spent nearly 2 weeks trying to get house martins in focus (I was on a family holiday so it was not full-time!). I found the 100-400 seemed to lock on better sub 200mm, post that it seemed harder, so then had to crop = worse images. Might have been me, not sure. I suspect the background also have an affect. I did try all focus points active against a clear sky, but that did not really work well for me unless there were multiple birds in the sky, so single points or the smaller multi point selections worked best for me. I think they were just too fast.
Anyway, I would echo Mike, go with fast shutter speed, S-AF, single point or multi point AF (not everything), be prepared for disappointment and occasional delight!
Ultimately I think this is a great little camera but it's not designed for BIFs, you can get them but keeper rate is low (for me anyway) - an EM1mkII or G9 is what we need, or possibly an EM1, maybe G80.
Please note I'm still very much the amateur and there are far better photographers on here who can provide some better guidance - if I find something that works better for me I'll let you know!
Good luck!