“Nuisance” in strata law is a legal term with very narrow definitions – but it could be loosely defined as something that causes another owner harm. When you think how long it took to get passive smoking accepted as a possible nuisance under strata law, then your cat and bird feeding probably isn’t going to qualify.
There is no default by-law on feeding stray cats or “bin chickens” but all you have to do is pass one. “Residents and their guests are not permitted to feed wild birds or stray or visiting cats or dogs on common property, or encourage them to cross common property to be fed on lot property” would probably do it.
Have an EGM, pass the by-law, issue Notices To Comply then have them fined when they ignore them. It’s time consuming but it’s a lot easier than trying to get NCAT orders by stretching the definitions in strata law.