Greetings, my fine feathered friend!
Whenever I start an animal portrait, I work on the eyes first. In fact, I spend more time on the eyes than on any other part. Why? Because if I don't get them right, then the entire drawing feels lifeless.
The eyes have to remain vibrant even from a distance. The best way to do this is to exaggerate the dominant colors. For instance, the tiger eye above has a very intense shade of blue around the pupil. Look at what happens to that blue if we take a step back:
You can still see it! When I work, I frequently stop and set the drawing across the room. Sometimes the colors are too washed out and I need to rework them again.
How do you create the illusion of round eyes? First: light. That small white sheen gives the appearance of a layer above the colors of the iris. Second: the folds of skin around the eye. The eye can't just sit on the face; it has to be held in place!