I just got my first bird, a grey cockatiel. He came from a breeder. Someone else in my family also got the same kind of bird from the same breeder. They can hear each other and often will be screaming at each other. At times my bird, Skye, will be fine being on my finger and perching on my shoulder, but other times he hisses and snaps at me. He does this in numerous places. But mostly in his cage. He seems to have gotten more aggressive since another family member got their bird. Advice? To have them stop screaming and biting/hissing/snapping.

P.S. He is always shivering. Why is that?