2 part question about my parakeet

Question
Our family has a male parakeet named Kiwi that we have had for about 2 years now, and I wanted to know about two things, I don't know if this helps but we had another bird that was a very aggressive male, but now he is alone, but anyway
1. Why is it that he occasionally shakes his tail feather and
2. Why is it that every other parakeet that I have seen, they have solid black eyes, but Kiwi has the white around with a visible pupil;
why is this?

Answer
1) Sometimes birds shake their tail feathers when they want to loosen their feathers up, or as a greeting when they are happy to see someone.  It would be the same as if they spread their wings- helps to allign the feathers.

2) Young budgies (aka: parakeets) always have all black eyes. As the birds get older, they will have a very visible pupil.

I hope this helps answer your questions.

-Maggie