I guess what you actually are asking is: 'who is going to pay for this extra, but obviously sensible added protection, not specified in the original contractual papers?'
Anyway, this will of course be depending on where you are in the world.
It might be defined put under general human safety rule, as a bird nest could obstruct the outlet capacity and give a dangerous situation.
I believe else that 'no' is the answer, the nearest comparison I can remember is the often general description of hygienic protection of water reservoirs openings against animal life.