I'm so sorry Prod, it is so difficult to get the right balance between space/freedom for your birds and security. If the hole was large it could have been badger, they have been know to climb fences as well to get at poultry.
I think it was a stoat as I saw one earlier in the year around about 5pm, which I know is unusual, and the hole in the fencing is only small. I am sure some of the calls must have got away as there are no dead ones and very few feathers around. What suprises me is that Gus & Sweetpea, the runners, were out of the pen so they must have flew/jumped 4ft to do so. There were no marks that I could see on Gus but quite a bit of blood on Sweetpea. I am going to bait some traps tonight and see if I catch anything......