I'm in a chicken facebook group and keep reading about people finding hawks mysteriously trapped inside covered runs (that have different kinds of netting on top, or even a roof!) After some searching, the owners find that the netting/fencing was compromised somewhere - either the overhead netting, or the fencing elsewhere (if it was chicken wire or something similar less sturdy). There was a hole, or it had pulled away from the wooden frame, or something, and the hawk must have pulled and widened it to get in. One person even swore they found a 3-foot gap they don't remember being there before. So I guess it must be a thing that happens. If it's something sturdier and hard to bend/pry open like welded wire or hardware cloth, they probably won't be able to pull at it and widen any holes (or create new ones).