It sounds as if he is trying to be dominant, or top of the pecking order, as it were. Highest bird = in charge.
This belief has been part of the parrot world for a long time, but it is in fact untrue. Birds do not really have astray turned pecking order n their flock like dogs have in packs or horses have in herds. However, the highest place is the most favorable, because it is the SAFEST place, the best vantage point from which to survey the room. Many birds bite when they are on heads, shoulders, or high perches simply because they do not want to come down and biting makes the hand go away.
If a bird bites when on shoulders/heads/anywhere else, he is not allowed in that spot until he learns to step up nicely without biting. Every single new bird I have ever brought home (I currently live with 28 parrots) has had to be taught not to bite when being removed from favorite places. It is an issue of manors.
That said, caiques are going to be one of the tougher species to do this with, so you are going to have to be extra strict and extra consistent. I suggest no longer allowing the bird on heads or shoulders.
Several years ago I called up Dr. Steve Hartman of the Parrot Univesity, the guy who invented the aviator harness. He is working toward the domestication of parrots, and I wanted to do the same. I will be honest and admit he told me I was naive in the questions I brought to him, but one of the things he told me is that he does not think caiques are good candidate for pets because of their aggressive personalities. Not just meaning that they bite, but that they do what they want when they want. He said they are great pet store sellers because they see a person, hop onto them, and run up their arm to their shoulder and the person is thinking "they chose me" when really they just wanted a higher seat so they took it.
So realize that what the bird needs is training and boundaries, but don't be surprised when that is harder to do with a caique than it is with a cockatiel