help! blood in poo

I'm new to chicken keeping and 4 days ago aquired 3 bantam chicks. They're about 12 weeks old and are all different breeds. This morning I noticed some blood stained poo. After watching them for a while it appears to be the silkie. She doesn't seem any different in her self, (she's always been the tamest and most friendly), but this is quite a lot of blood not just the odd spot and I can't find anything in my books or on the net to tell me what's wrong. They were all reared together, and I have been feeding them growers pellets, they live in a small henhouse with an attached run and we let them out for an hours or so every morning and evening for a nose round the garden. Can anyone help? I know we've only had them a short while but we've become very attached to them.

Have a look on these pages to see if you find one that looks like yours or rather your chickens   You will find lots and lots of different poos most of which are normal.

http://chat.allotment-garden.org/index.php?topic=17568.0

sorry, just realised they are on growers! Just check to see whether unmedicated or not

get them all treated, they can pick it up from wild birds.