We have never lost an adult chicken to the sparrow hawk but various things have taken our chicks - including corvids, stoats etc, but probably the sparrow hawk too. I'm glad they take magpies as I'm not very fond of them - they ripped out all our swallow nests one year. We have some small breeds which are about the same size as a silkie, so they might be ok........... Sparrow hawks seem to prefer to take their prey from trees, hedgerows, hanging feeders etc as they are a bit clumsy close to the ground.