This is too cool...
About 80% of the time I'm shooting birds, I have things set like so.
AV, Partial metering, plus 1/3 EC, wide open aperture.
Well,. have you found CFn I-14 yet?
Set your camera to these or your own "usual" settings,..
Then register CFn 1-14,.. and now any time I press the * button, my camera will switch to the above settings and autofocus,, and wait for me to shoot.
As soon as I let go the *, the camera switches right back to whatever other settings I had..
So if I set up to use spot metering, with a stopped down aperture for more DOF, in manual mode to get a stationary shot, all is calm and normal using the [AF ON] button,.
Suddenly a Green Heron erupts out of the foliage and takes off in flight,.
Normally I have no way to get the shot, metering is impossible, I can't adjust manual exposure fast enough, etc..
With MkIII and Cfn1-14, I simply move thumb from [AF ON] button over to the * button and I am shooting exactly as I would set up for BIF shots by moving my thumb a 1/4 inch!
This is awesome!