I think you are, perhaps deliberately, missing the point Slowclimber. If the CAA issue a document in which they detail all the various methods of discouraging birds from becoming a hazard and which explains which methods work for which species or groups of species; then I expect their inspectors to understand said document. Not understanding that corvids may not be deterred by long grass is about as ignorant as assuming that playing the herring gull tape on the BABS will have any effect on wood pigeons. The whole point about bird control is that it requires a certain amount of ornithological knowledge. Sadly too many management types think it is sufficient to give someone (usually a fireman) a vehicle, a tape player and a set of crackers and then expect to achieve a bird free environment.