Joel,
thanks for the explanations.

If you use the center focus point only in AI Servo, will the camera still use the other focus points to track the bird? It is not always possible to keep the center AF point on the bird at all times. Or is that something that only more advanced bodies do (7D and up)?

Will try on my 600D/T3i as soon as I see a bird flying, or maybe use the dog as an easier test object :-)

Thanks,
Arnt