Birds that are puffed-up, ruffled, or appear unusually sleepy could be sick. Look for bright eyes. The eyes should be clear, without any discharge. The eyes should not appear swollen. The nostrils should be clear, the same size and shape, and without anything blocking them.
Budgies commonly get scaly face, and it is caused by mites.
The bare facial patch on a Macaw should be clear and white, redness sometimes means the sinus cavities are infected. Look at the beak. The upper and lower parts of the beak should meet each other cleanly. Crooked and overgrown beaks can be signs of hidden illness. Look for shiny feathers, and the bird should not have bare patches on the chest.