Too bad it can't say Naruto-sama's name, useless bird.
You may aswell release it back into the wild where it belongs if you aren't going to teach it anything useful, Believe it!
Birds can't rotate their eyes very much/at all and thus have to bob and twist their head in order to focus on things. So in order to get the same range of vision as a human, instead of moving their eye muscles they don't have, they move their head and neck instead!
This is in part true. Bird eyes are a lot less mobile in their socket than human eyes. But I know one answer for pigeons specifically (idk how well this can be applied to other birds as well).
They do not see well when their head is moving (could be that they're lacking a optokinetic nystagmus due to immobility of the eye within the socket but this is just an assumption) so they keep it still for as long as possible even when walking and then have one quick movement of it. That way the don't see properly for the fraction of the time they would have improper vision if they were to keep their head moving at the same pace of their body. That's the typical bobbing you see within them.
And I totally love how you just asked a behaviourist something about physiology haha those are two totally different fields. I hope I could help you out a bit c:
You are asking good questions right here. There's one thing I could think of that makes them do that. Bobbing one's head in parrots is a common gesture of courtship. It's common that animals, not only birds, use such gesture even when they're not currently courting/sexually aroused but even when they're aroused in a non-sexual manner. It's a displacement activity I guess. You can call it a habit if you want to.
Both are great subjects. You'll have to have a passion or knack for them though if you want to stay interested. There's a reason why all chemists and biologists don't seem right in the head xD
I don't have source but I'm sure someone could find it. But a parrot was the first animal to ever have been recorded to ask an existential question, it was "what colour am I?". Parrots are very cool animals.
Bodeejus was right. It was indeed Alex the african grey. There's tons of research regarding him that can be easily found by searching for the author Irene Maxine Pepperberg.