This is a large flock of Royal Terns vacationing during the winter along the Gulf coast of Sanibel, Florida, but some of their relatives will migrate down to the Caribbean. They scamper along the saltwater beach in front of the tourists while making a shrill sound, then will scatter and regroup once the beachcomber walks by. During the breeding season, which runs from April through July, this 18 to 20 inch bird’s black head plumage turns all black (not spotty like in the picture) and they can be seen as far north as Maryland.