This is why you put a little bell on the cat's collar. That way it can't really sneak up undetected.
Additionally, bells don't impact the other damage outdoors cats do to gardens, the deceased life expectancy, and the increased chance of disease.
Do not let your cats outside.
Saw this with the neighbours cat, little sod is so smooth he doesn't ring the bell until he pounces and by then the bird already knows it's in deep shit.
My pair are indoor cats - they live longer and we are near a very busy road.
- local bird, probably