As wim says, burst speed can't be improved with CHDK, but the fastest you can go on these Digic cameras is when you have
- RAW and DNG disabled,
- low ISO (200 or lower on my camera, above that noise reduction software kicks in and slows things down),
- Tv fast enough compared to burst speed (duh),
- a clean freshly formatted SD card (a large amount of images and/or filesystem fragmentation slow down write speed),
- a fast SD card,
- output image size set equal to shot image size (usually this means full resolution JPEG) to avoid scaling
- medium JPEG quality selected to reduce file size (writing time); full quality images can be very large.
and to squeeze the last drop of speed, but sacrificing a lot of image area, making it harder to catch a moving target:
- use Canon's cropping set as high as it goes if your camera has that feature (it's called the digital tele extension feature or something like that) and match image size to the crop to avoid slow, unwanted scaling (color of the T symbol on screen changes when the camera scales up, that's when you know your resolution is too high).
And it's true, motion detection works perfectly with flying birds, at least near nests where you know they are going to fly in frequently using the same route... you can get amazing in-flight closeups since you don't have to be there scaring the birds.
