Seems to be a pretty brief form to fill in. I am guessing they will not really be interested in those just registering a few birds, but in the event of a major bird flu outbreak in your area, they might be looking at breeders or smallholders. I can’t see aviary birds being too much of a risk. Perhaps racing pigeons who fly free are more of one
My little lot have a roof over their head year round and are kept in when bird flu is about, because I don’t want them getting ill. I’ll register them, but I think I am a responsible poultry keeper anyway. Sorry to be cynical, but it makes as much sense as the dog licence scheme. When it was abandoned in the late 80’s it was estimated about half of dog owners didn’t bother.