I personally think the 28ga. AA sporty clay loads w/#8.5 shot are some of the best rounds ever factory loaded. Opinions differ; I knew of a couple of people who shot the Federal 1oz. 28's enough to crack the frames of their 1148 Remington's years ago and swore by them. Federal does not make that same exact load any longer. I never considered that quail took that much killing, just accurate shooting. Again, being personal, I see zero reason to shoot a 1oz. load in a 28ga. gun, even one built on a 12ga. frame like some Franchi O/U's were. AA 28ga. once-fired hulls are readily marketable as well. Some skeet shooters will pay up to $0.15 ea. for them. The Winchester AAHS 28ga. hull is the top dog hull for reloading, bar none.
AA20's have always been one of the best rounds out there in new factory loads since their introduction with then red hulls. 7/8oz. shot is adequate for most any bird shooting up to feral pigeon size. My personal favorite load for that application is the Federal Game loads in #6 loaded w/the two piece wads they never sold as an individual component.
To directly answer your question, I don't think you would be remotely handicapped using AA target rounds on birds up to feral pigeon size.
Addendum: I'd totally forgotten the use of one once loads for flyers in 28ga. or 20ga. races that Eightbore mentions or ducks as Jon mentions & Francis Sell was also a big advocate of the 20 for ducks. Personally, I have always used 12's for waterfowl, still do. FWIW, in the older loadings before some of today's newer powders were brought into play, one once lead field loads in both 28ga. and 20 ga. were slower than the regular target loads, didn't pattern as well on the many sheets of butcher paper that a bud & I shot and drew circles and counted the holes in and quite simply only delivered more recoil. I have always shunned 1 ounce 20's for that reason. In places like South America where one can shoot a lot of ammunition dove shooting they will quickly beat you to death in a light weight double gun, but you can shoot the 7/8oz. rounds until you get tired of shooting and have no sign of a bruise at all. Much better on both gun and man. The older AA12 Super Pigeon rounds were some of the best 12ga. flyer loads; they even made them w/#6 shot. I've no experience w/the AA20ga. flyer rounds Eightbore has. Comments above are addressing 1oz. field loads.
