In reply to tmawer:
I think you probably already know the answer to your question as well as what follows (which partly re-iterates what my BMC Cymru colleague Elfyn has just written):
In Wales, (although I expect exactly the same principles apply in England too), seasonal restrictions designed to minimise disturbance to nesting sites are usually agreed between BMC Cymru, landowners and Natural Resources Wales. By climbing during the agreed restricted period, climbers may then risk committing a potential offence under the Wildlife and Countryside Act 1981, namely 'intentionally disturbing Schedule 1 bird species at or near a nest site'.
More specifically, it is an offence under section 1(5) of the Act to either intentionally or recklessly disturb any wild bird included in Schedule 1 of the Act while it is building a nest or is in, on, or near a nest containing eggs or young; or to either intentionally or recklessly disturb the dependent young of such a bird. Relevant evidence to prove the offence may include anything tending to rebut claims of accidental presence near to the site. Climbers roped up on a nearby route would probably fail to prove an 'accidental presence'.
Outside any seasonal restriction dates, the agreed advice is that common sense should be applied if birds are present and appear to be seriously alarmed by the presence of climbers. All climbers should act responsibly and if it is suspected that there are raptors, choughs etc. nesting on any crag, then simply climb elsewhere.
Peregrines show considerable tolerance to human activity, but will not tolerate human disturbance near the nest or from above. When a peregrine is flying above you, making a ‘kek, kek, kek’ call, then retreat immediately as this is a clear indication that you are causing disturbance. This isn't necessarily the case for other raptor species such as merlin or red kites, both also Schedule 1 birds who are far more intolerant of any human presence anywhere near a nesting site. Merlin often nest in tandem with peregrines - at least here in Wales.
In any event it is the climber’s responsibility to check for up to date information before climbing. The BMC’s RAD may provide details of these restrictions (if known), but this is no guarantee. In the absence of any known BMC agreed seasonal restriction, then the potential for committing an offence under the 1981 Act still applies. On this the law is quite clear. Any such offence against peregrines can attract fines of up to £5,000 per offence and/or a custodial sentence of up to 6 months.
Schedule 1 birds are, generally speaking rare in the British Isles and subjective assertions that 'peregrines are becoming more common' will not be a defence if prosecuted.
This is a very useful summary of research with regards the effect of human disturbance on a number of bird species: http://www.snh.org.uk/pdfs/strategy/renewables/birdsd.pdf
HTH
Dave
(BMC Cymru Local Access Rep)
Post edited at 14:40