What does this...

[palmerchick]

We have 3 RIR in a pen with our Indian Runner ducks, they have grown up together and always been fine. Today we found one of the RIR with its head pulled off, but none of the other birds were injured. This happened through the night, we have a coop with chicken wire enclosed run. No holes in the wire, or around the outside of the run.

 

[Egghead_Jr]

A weasel will eat just the head and if you've chicken wire without closing the birds in the coop at night can easily fit through those holes to get to your birds. If the RIR was roosting near the side of fence a raccoon could have reached in and pulled the bird head through. Depending on where the bird's body was (edge of fence or not) would be which of the animals I'd guess done the deed.

I've lost birds to various predators (skunk, stray tom cat and mink) it's never fun. The daytime attacks, skunk and cat- pretty sure neighbors dog got a wee cockerel too, I can't fully avoid but never a problem with mink or weasel in the night anymore as we close the coops each night.