At the risk of not sounding very helpful, I suggest that the best way to answer this question is for you to take your camera out and just start experimenting. It's the best way to learn in my own experience.


Obviously if you want sharp action, a faster shutter speed is good, if you want motion blur, slower. Just what that speed may be depends a lot on how fast your bird is moving, what type of movement it is (e.g. glide vs. flapping wings). With regards to the fish, here's a shot I took about 18 months ago at 1/200 - it's on the edge of stop action and motion blur as you can see by looking at the fish in the bill and the water drop close to the surface. Hope it helps a bit. (I took this with a 2x extender on the 100-400mm at 400mm, effectively 800mm. Considering how this combo is often spoken about as being less than optimal, I was pleasantly surprised by the result, with manual focus and all).


AI Servo is good for birds coming at you or flying away, yes. I like to use higher ISOs on low light days to keep shutter speed fast.


Camera: Canon EOS 30D
Exposure: 0.005 sec (1/200)
Aperture: f/11.0
Focal Length: 800 mm
ISO Speed: 100