why is unrealistic? I think it would be good.
DLC packs don't exactly load up on animals. Even the animal-only packs only have seven habitat species and one exhibit species. Now, I wouldn't be surprised if they gave us extra for an aviary pack, since a brand new game feature isn't very exciting if there are only a few species to use it with. But twenty sounds way too optimistic, lol.
That said, if the aviaries themselves are added as part of the base game early enough and an aviary DLC only exists to give us a variety of options, we could expect to see birds added in later DLCs.
My guesses for an aviary animal roster? I bet we get a large fruit bat and then the rest are birds. I'm pretty confident we'd get a bald eagle and a macaw or two. Definitely an owl of some kind, but hard for me to decide on a species, there are a few majorly iconic ones. I think the snowy owl would have a good shot since it's iconic and would add diversity to the arctic selection. I wonder if lorikeets are a possibility, since walk-through lorikeet exhibits are so popular these days. Some kind of wading bird, too... There are so many good choices, it's hard to guess!