Maybe someone chime in, I dont have any experience with snakes. Hopefully your game camera will come up with something. Does not look like any bite marke though.Something get around it and suffocate the bird?
Get a game camera. Not knowing what predators you have or area you live makes it hard to tell. You could look at dead hen and look for bites at back of neck head area, small bites...weasel family.
Sorry for loss.