As far as I understand it, rogue Capercaillies are now also covered by the Schedule 1 "disturbance" laws. Anyone going looking during the breeding season and being on the end of a 'displaying' Capercaillie is, I believe, potentially breaking the law. If you aren't there, the bird isn't wasting energy 'displaying' to you. If the bird changes its behaviour because you are there, that is apparently how 'disturbance' is defined with regards Schedule 1 species (from what I've read).
Given the level of 'known' disturbance via photographers etc (photos posted online etc), how much goes on 'unknown'? Hardly surprising the numbers are dropping when folk can't seem to help themselves, trying to get the exact same photo as everyone else has - male Capercaillie tail fanned, head back, beak open.
I've never seen a Capercaillie and the only time I've looked for one was on a September holiday I won with Heatherlea from a mini-bus. Birders can hardly moan about certain wildlife crime when birders themselves are also guilty of a wildlife crime (whether you agree with the laws, as is, or not - they are what they are and they are there for a reason). For around roughly 2/3 of the year, it isn't illegal to actively look for Capercaillies, though they are much harder to find.....but no, that 1/3 when they are 'easier' to find is when folk have to go looking.