The bird on the right (yes, it's me) as you can see, I have my head feathers up. Chances are I'm surprised, curious, or alarmed. I'm also looking kinda skinny. That has nothing to do with my diet, (which is fine) like his crown feathers, it means I'm alarmed, surprised, or curious. As you can see on the picture on the far right up there somewhere, I'm sort of puffed up. Relaxed is what it means. Our feathers add to our size. When we sleep, we become even more puffy.
On to the multi useful beak!Beaks are used for eating, preening, checking things out, climbing, and defense. Shells of seeds are punctured and and the delicious interior eaten, and feathers are cleaned and prepared for flight. You can tell, birds don't have hands, feet yes, but we cockatiels don't use them to pick things up. Instead,we use out beaks! So wires beware! Hmm, wires are chewy...uh...
Defense! Of course, if meany hands are forever in the way, they will promptly be bitten. So pleeaasssee be careful. Nice, too.