I think I have a rat who has found my chicken pen. I have found where it has dug under it, not a very large area, maybe 2-3inches deep and about twice as wide. It comes in at night and was stealing 6-8 week old silkie chicks from the pen. Will not bother the full grown silkies, half grown RSL's,half grown NHR, and full grown banty cochin roo. Took the chicks right out of the hole he dug and then came back looking for more a couple nights later but I put the rest of the chicks in the brooder again. I have seen a large rat in there, that is the only thing that could be getting in that hole. Tried shooting it but it is gone as soon as it hears the door to the house open now. That is the only way into that chicken pen right now is through that hole he dug. I am about to concrete the floor in it so he can dig under all he wants and not get anywhere.
There are other predators that could get through a hole of that size. (weasels and minks) but they wouldn't hesitate to take one of your full sized birds so I am guessing you are right in that the rat is your problem. Have you ever thought of just setting a snap trap in an area that your birds can't access it? I think that would be a fast and easy answer to your problem.
A rat will do that, and they are not beyond attcking your larger chickens if hungry enough. Set some traps!
