Certainly not an unusual bird (we see this all over the southeastern U.S. coast, and elsewhere), I had not seen this particular wing-display behavior. I received a very informative email from the always knowledgeable Peter May on this behavior. He confirmed that he sees this type of display once or twice a year, and based on the wing position, and the bird's orientation toward the sun, feels that it is "almost certainly a behavior to increase heat absorption." The odd thing is that it is not generally seen during cooler times, but more likely under mid-day, hot conditions, often accompanied by the "gular fluttering" which many animals use to get rid of excess heat. His working hypothesis is that the purpose of this behavior is to increase body temperature, perhaps in order to help get rid of skin parasites. If anybody has any additional information or knowledge on this behavior, please email me.