Animal substance seems to be the first food of all birds even the granivorous tribes.
I think people are born bisexual and the make subconscious choices based on the pressures of society. I have no question in my mind about being bisexual. But I'm also a hypocrite: I would never date a girl who is bisexual because that means they also sleep with men and men are so dirty that I'd never sleep with a girl who had slept with a man.