Hard question though is there any animal in each DLC that you would trade for an habitat birds?
Honestly, while I don't dislike any animal we've gotten, there are loads that I wouldn't miss in the slightest if traded for a bird. Hell, in some packs there are even multiple species I'd choose, especially with how lacking in diversity the last three animal packs have been.
Arctic: Arctic Wolf or Dall Sheep -> Snow Goose
South America: Llama -> Roseate Spoonbill
Australia: Keep as is, every animal here is essential for the region.
Aquatic: Also keep as is.
Southeast Asia: Proboscis Monkey -> Victoria Crowned Pigeon
Africa: Keep as is
North America: This one's pretty hesitant. As much as I love the beaver and arctic fox, neither are nearly as common or needed as a bird for North America, so either/both for -> Wood Duck and/or Burrowing Owl
Europe: This pack's animal roster just wasn't for me at all so it isn't really my place to comment on it I guess. Though if pushed I'd totally ditch the ibex or badger for -> Western Capercaillie
Wetlands: Wild Water Buffalo, Spectacled Caiman, and/or Nile Lechwe -> Pelican species, black swan, mandarin duck, white faced whistling duck, scarlet ibis... way too many options here. In hindsight, this
should've been a prime pack for birds.
Conservation: Scimitar Horned Oryx -> Guam rail, mandarin duck, African pygmy goose, nēnē
, selfishly a South Island Takahē, once again loads of options.
Twilight: Red fox or Striped Skunk -> Move the little penguin up here (kiwi could work too, but I'd miss the Oceania pack's statues for it lol)
Grasslands: Caracal or Blue Wildebeest: Grey crowned crane, helmeted guineafowl, southern ground hornbill, secretary bird, etc... once again a pack that should've had multiple birds.
Tropical: Like NA, this one's a bit more hesitant. I love every animal here but I can't say I'd be upset in swapping the gibbon or AWM -> Scarlet Ibis
Arid: Hoo boy... I'd swap the dama gazelle, addax, black rhino, sand cat, and/or wild ass -> for any of the birds suggested for grasslands in a heartbeat.
Oceania: After safely delivering my beloved lil' blue to Twilight, there's an open spot here for a nēnē, Victoria crowned pigeon, cape barren goose, or black swan
Eurasia: Bye bye saiga! Maybe ditch the sloth bear too (as much as I like it personally I'd happily trade it for another bird) -> mandarin duck, golden pheasant, Himalayan monal, great argus, white stork, etc...
Barnyard: Alpaca, donkey, and/or sheep -> Helmeted guineafowl, domestic duck breed, and/or domestic goose breed.