In reply to Ennerdaleblonde:
I've only climbed on Pabbay (in late June) but I was surprised how little overlap there was between prime climbing terrain and nesting ledges. Looking back at my photos (we took kayaks so had a good look from the sea too) there's almost no guano at all on the main crags. I don't think that's because the birds have been scared off, there simply aren't enough suitable ledges; very different to Hoy or Cilan for example. So I don't think there's much rationale for a seasonal climbing ban here, although climbers exploring new areas should always be cautious. Given current population trends the bonxie colony on the east end is perhaps the only concern but there's no climbing in that area.
There probably is a conversation to be had about the number of climbers camping and toileting though. The NTS warden was on the island at the same time, so they have an eye on things, numbers felt ok but if they doubled, say, I think you might need a rethink.
Mingulay is obviously much bigger and complex. As I say, I haven't climbed on there but I have been on a birdwatching boat trip right round the island, through the stacks, arch etc. My impression was the main seabird areas & are not climbed on, mostly because the ledgey terrain (e.g. Biulacraig) that is good for nests is not so good for climbing, while the stacks etc are pretty inaccessible even to climbers. So while there's perhaps some scope for formalising the separation of these zones, with the tiny numbers of people doing exploratory new routes and the way the Scottish access code works, the current approach as outlined by Robbie's excellent article would seem sufficient at least for now.