[eeyore]

I would suggest that you use f5.6 for anything which is perching or relatively stationary, or flying at right angles to the shot, as this will lead to a nice blurring effect in the background. f8 is probably best for birds flying towards you were you will need more depth of field. I would advise you to use one shot AF for stationary shots, and switch to servo mode for flight shots. Canon AF is very good and will almost certainly beat manual focus for anything that is moving. For perching shots select an af point to put the point of focus on the subjects eyes, while for flight shots either select the centre point if the background is confused or select all for shots against plain backgrounds such as the sky. For more detailed advice you could do worse than check out Andy Rouse's "Digital SLR handbook", and/or Chris Gomersall's "photographing wild birds". Hope this is helpful.