Male parakeets in the wild are cannibalistic. When you make this noise his hunting instinct kicks in. But parakeets aka budgerigar are very tricky. They will sort of pretend to be playful before they kill. Just a bite in the neck to a fellow parakeet is all it takes because they are fragile and have a powerful bite. Now for the real reason. He is just happy, being playful. They are fun birds so enjoy.

Your budgie is just being a...budgie, its what they do. He/she is having fun and being playful. Budgies love attention so whilst you are doing what you do its his/her chance for human company.. If your bird has a brownish cere then it is a female.

I have a male parakeet, I don't know how old he is. He does this only occasionally, but if I move my face right up to his cage and make bird noises with my mouth, he makes this 5 or 6 chirp trill, can't really describe it. As he's doing this, what looks like a sideways mohawk forms on his head, and he jumps up to the side of the cage, and comes up to me and kind of nibbles on my nose... does he think I'm a female parakeet, and go into mating mode? Is he just happy to see me, or does he want to kill me?

Don't know if this makes a difference, but he'll only jump on my finger if he's hanging on the side of the cage, not if he's on a perch.