The yellow "eye" is actually her eyelid. Peregrines have great binocular vision
but they use monocular (one eye) vision when they are focusing on closer items or are
looking at details. That's why they cock their heads when they look up. It looks
like Princess is sleeping, and in this case she is, but you will frequently see
the birds napping then they open one eye. Its not laziness, they only need one eye
to look at what is close to them. If its something further away, or moving fast,
the other eye will shoot open and they go from napping to high alert. Neat to watch.