Wow I think this is what is happening to my chickens! Rooster was beheaded this am with the head laying next to him not eaten either. A couple of my hens have marks on there necks. I have lost almost 15 this week. First thought it was illness, could not find any marks and not eating mash, only scratch. then as the week has gone on more injuries. the hen i put in a dog kennel is doing great thought she was sick. This has been a confusing depressing week. Took one hen to lab for autopsy, waiting for results. But I am sure it is a weasel now on top of whatever else.
Oh my!! They will come back everynight untill they cant get in the pen house anymore or untill they are all dead. They can get in a 1 inch or bigger hole. Mine got in thru the roof line where it meets the wall. I had stuff leaning against the building and they climbed up it. Im so sorry, its devistating. I lost 9 in one night including 3roosters. I still have 2 but I made sure nothing can get into them at night. They suck all the blood out if them. Thats why the marks. So sorry