I am royalty upon ice, yet my kingdom melts in summer. What am I?

Tell me, How does the ocean greet the shoreline?

As I am, a green symbol of vitality and endurance But swap my second and third, then spell me in reverse and my meaning changes to make something weaker

Snow upon water, long of neck, approach with care, or earn a peck.

I drift where lesser wings grow tired, my piercing gaze is much admired. No crown I wear, yet skies I claim, a sharp-eyed hunter, known by name.