I'm not sure it's any help, but I remember a late 90s Vauxhall Rally of Wales; and in the programme's spectator information it stated 'no spectators at Hafren - due to birds nesting'; groups of speccies disturbs them, but rally cars flying through full chat don't.
My only issue is there are plenty of walkers paths nearby, including a picnic site not far from the famous Hafren hairpin.....And they don't seem to be restricted during this time of year.