Fun fact: In the Bastion's lore, it is stated how he was inactive for many years in the forest when all of a sudden he was reactivated. It isn't stated by whom or how he was reactivated, which means that the bird could've potentially landed on his ON button and awoken a robot designed too mow down crowds of people.

So Bastion & the bird have an Ultimate Chimera-type deal going on? I kinda like that theory.