"Is it love? Or dependency, survival instinct, interest? Need of some sort of society, interaction? Boringness?"
Definitely love. Or at least in the case of my bird, and in the case of many people's pets. Usually dogs.
See the story of Hachikō, for example. Hachikō waited for the return of his owner at the Shibuya train station, even after more than 9 years after the death of his owner.
What is this, if not love and loyalty?
"Some humans don't judge either."
I did not wrote "every human", nor "all humans".
I wrote "humans do", which means humans do in general.
"And some animals are dangerous, or stupid."
Just like some people.
"Don't underestimate humans. You may need them."
I don't underestimate humans. There are a few good persons, but I have my own opinion about the majority of humanity.