They weren't small birds like common chirping beasts; they were colossal flying monsters, each easily reaching the size of a small dragon.
Yet, even with such massive, heavy bodies, they could fly with incredible agility and move at speeds that defied logic, thanks to their species mastering the wind element in a few distinct variations among their flock.
The pure lightning-based monsters would work as the main brute strength and bulk of their aerial army, while the highly agile, wind-based monsters would act as their tacticians and flock leaders.
William knew that the lightning-based birds would naturally surround their massive bodies with a dense, crackling shroud of electricity to defend their flesh against any incoming ground attacks.
Trying to focus his offences on them using his raw darkness element wouldn't properly work right away; the opposing elements would simply cancel each other out, and it would take far too long to yield any tangible results.
