I've asked myself that same question. I could see how they got in,but how in the hell did they get out with a bird? Never figured that one out. That's when I bought my cameras.
You could drop some sand or fresh dirt around the pen as well. You might get a track mark and identify it that way. I have a night vision camera inside of my 70ft run as well as 2 cameras that record all activity on both sides of the exterior.
Have you seen any fox activity around you? Any carcasss' further out away from the pen? I want to say that a bobcat wouldn't make repeated trips and would be flying solo. Coons would hit you in groups but probably wouldn't have the muscle to rip wiring apart. Whats the common predator you've...