We have had 2 flocks killed by fisher cats DURING THE DAY. We live in southern NH. They are VERY smart. Make sure your coop is extremely predator proof. I thought mine was, and the %#$@&*&%$ came up the side of the building, into the eaves, and down into a room next to the coop. It found a small hole in the floor (mouse size) and got it's slimy little hand through it. I don't have to tell you the rest.
We did not have chickens for 8 years after that. I did not want my kids to go through it again, and the dog was almost attacked as he tried to protect his family.
We now have 6 week old babies and they are in their run when we are not home. I put up 12 gauge wire fencing over the top of the run. It also has wire under the dirt floor that attaches to the sides and goes up 7ft to the top. My husband says an army couldn't get through it. No messing around this time!!