its what cats do... fair play to a cat if it can catch a bird its done what it was designed to do. Horrible i know but there you go the serengetty in your back garden - dont kill the cat you are evolutionally better than that....
I don't want to kill the cats (I'm quite partial to a nice cat), but I just want their owners to have a little more responsibility for their actions. ie bring them in overnight and lock the cat door so they aren't out yowling all night long, shitting all over other peoples gardens and at stopping them killing birds during the night. In the day its a little different - a bell should help a little bit and at least the birds have a fighting chance rather than being poached from their nests.