I suspect there isn't much we can do, but am just after any advice about if we can make our two cats any more 'noticeable' to the local wildlife. They already have collars with bells on but that doesn't seem to be stopping them catching birds. 
It doesn't help that there are loads of birds around at the moment as next door have just installed a big feeding station in their garden, right above a bush that the cats make a beeline for, hide in, then pounce when a bird goes onto the ground to hoover up any spare food- it's almost too easy for them!