the Sedge Warbler challenge

since getting a digital SLR I have tried to capture song flighting Sedge Warblers on the patch each spring; it is a constant challenge; a fast flying small passerine, only in the air for a few seconds and moving erratically about in height and distance so the AF system on the camera has a real problem that is on the odd occasion when you can actually find the bird in the lens before it plummets back into the reeds; today for the first time I tried with the 1DIII plus 500f4 and 1x4 converter; for every shot with a bird in the frame of course there are 10 without and for every one in focus 20 that are not but this is a severe challenge; it does however produce just as good results in arm muscle development as an hour in the gym!