In reply to GStone:
Thanks for flagging up - though they are Jackdaws, not Ravens. Much smaller, with a grey head. They nest in a lot of crags - on grit lawrencefield and millstone are especially popular.
About now, the best way to avoid them is listen for the chicks - often easily heard, or just sit and watch for 10 minutes before you climb and see where the adults are going in and out.
The signs here last year were for Kestrels (they're not here this year). Jackdaws are pretty tolerant of people - I've watched them going in and out of nest sites while people are climbing very close by (indeed the Kestrels were also impressively tolerant last year given how busy the quarry gets, and not just with climbers!).
Kim Leyland
(BMC Peak Area nest monitoring volunteer)