I'm not so sure a raccoon couldn't pull those birds through the holes. Those are not full sized hens. You'd be surprised how compacted a chicken could get .my only point in mentioning the size of the openings was that even IF a very small raccoon got into the pen it would have had to get out too with 3 chickens. the chickens most definitely can't fit through a 2x4" opening. same goes for a mink or opossum. so whatever it was either came through the fence then took the birds out a different way or came in from the top and took them out that way too. from what you've described from the scene it def doesn't seem like the predator ate the chickens in the pen or there'd be more evidence or a carcass. i'm just trying to save OP some money if the fence wasn't the culprit but was instead the tarp or other entry way.