Restless leg syndrome is a neurological disorder affecting up to 10 percent of people in the U.S. Also known as Willis-Ekbom disease, it may show up as an irresistible urge to shake one or both legs while lying down to sleep at night. I’ve found no sources suggesting that it also plagues birds. Probably this Willet has some kind of cramp in its knee or foot, or something stuck between its toes, that causes it to shake its right leg vigorously while standing on the other leg with its beak tucked into its back in the sleeping position. It’s remarkable that the bird is able to maintain its balance perfectly during this action. After several repetitions, the bird’s leg remained quiet and the bird slept until the tide rose to its knees, at which point it flew off. I’ve seen Willets frequently at the park, but usually in groups. This one appeared to be alone.