The Hunger Games

In Conflux, the Mage Guild is built on turn 1, so spell books will also be available to warriors. There are tons of options in general; I just gave the simplest one. There are even 40 birds by the end of the week.

I gave the simplest one :)
in all your variations, of course, the external dwelling is also taken, but with a big loss of meat.
On week 1, it's easy to build level 2 magic in the secondary town (although you could also find Lightning Bolt in a Shrine or have Alamar arrive).
And it's easy to level up magic to +3+4 in a week even on a not-a-pahan, but a scout hero. Or find an artifact for spell power.
I.e., having a Lightning Bolt dealing 100-200 damage, the mage goes into the bird external dwelling with 6 fairies. Easily takes out two birds; if you play well and level up the mage, it could even fire a Lightning Bolt 4 times, dropping 4-5 birds ;)
Mana needed, if without air magic = 10*2 or *3 or *4. I.e., 40 units max. Imho, a trivial matter.
The simplest is to send a pahan for this — he'll thin them out, and then head off somewhere to replenish mana or keep running, and whatever birds remain, any scout hero will clean up.