Rats

How have you enclosed the chickens?
Recommended is wire which is buried as an L shape at least 1 spade depth and 2 spade width to stop them digging in.
You should see round holes where they are getting in.
Compost bins wired underneath as they are cosy places to nest.
You can use wire cage traps, but these can be triggered by mice, you the have to humane kill afterwards.
You can use large snap traps. Glue the bait onto it, be careful setting them as the springs are heavy. Make sure the chickens cannot get to these as well as wildlife. Propped up overturn bucket helps. Check daily.