Why I think this means a bird pack next:
So far the exhibit system seems to have been limited to amphibians, reptiles and invertebrates. With flying mammals now in exhibits, I imagine flying birds is to expect to show up in them too.
This is an important step, if they want to do an dedicated bird pack without breaking their habit since SA of always including an exhibit animal.
I don't think they are going to do an exhibit animal only pack. They might just keep to 4+1 or 7+1 or maybe do a new combination. I'm more likely to think it still will be a bigger amount of habitat species than exhibits, maybe half/half, but that is just me guessing.
Habitat birds is already a thing since they one of the game, and it is not hard to come up with 7 good choices that doesn't need flight, where some will be easy to make and others more unique to what we got.
I imagine birds like a pelican and secretary bird, maybe Kiwi are going to be the popular choices. That might even convince the mammal mob that a dedicated bird pack is nothing bad.
And why will it happen now?
A bird pack will probably be a bit more work than most DLCs we have seen in a while. But with two animal packs in a row, with fairly easy to do species (besides from the Siamang), I imagine the animal team should be able to deal with it.
With both one bird (so far) added this year, and only one last year, the lack of birds can't be ignored anymore, only a dedicated bird pack could get us back on track. And when we now have seen yet another mammal, in a system that feels more like it was made for birds they need to take action, if they don't want to end up with a lot of unsatisfied customers soon.
I got even more arguments, but this post is getting long now