I was at Crag Lough yesterday, I was warming up on Hadrian East, and got to a point where my ample frame wasn't going to fit through a narrow gap about halfway up (where there's a large block on your left), I lowered off, went round to the top and abbed down to retrieve my gear, to find a nest with several speckled (crows' I believe) eggs in a tiny cave, about 6 inches behind my gear.
Later on when I was checking to make sure I hadn't left anything behind before I left, I did see a couple of crows fly out of the cave.