I can't poison them,as they could well die in the chicken run. They have tunneled under the decrepit barn. Chicken run uses 1 wall of barn as 1 wall of outdoor run. I was going to try
@BY Bob 's method of dry Ice, but I don't think I can possibly cover all the access holes. Maybe I will just cover as much as possible, and the dry ice may kill off some & lessen the #? It is hard to explain, but it is a pole barn with board & batten on outside, but part was horse stalls for draft horses, and on the inside there are 2x8x 10s, and there is a gap between inside & outside the diameter of telephone poles (the 'poles' in the pole barn) that the rats can access, but I can't.
I did get the 'mother & father', but won't be long before the others are reproducing...and there are lots of them (?maybe more than one reproducing pair in a colony, so only got 1 set??)
dirty little buggars!!