I've completed the game, and I'm wondering/hoping if I missed something important connected with this fascinating creature of the developers' imagination.
We know that Songbird was protector of Elizabeth and her only so called friend. It was summoned by flute music. Songbird was nearly unstoppable - killing him by drowning in Rapture depths shows that. His death also reveals that it had violet blood. Songbird's eye colour depends from its mood there was green - peaceful, yellow - alarmed and red - aggressive.
How was it created? Does it eat anything? Was it originally human?
Am I too curious and I should accept that this is only a game and some questions aren't going to be answered?
I've never played Bioshock 1 or 2 so I don't know anything about the Big Daddies.