The sandbar off of Coast Guard Beach, part of the National Seashore in Eastham, was filled with Arctic Terns. They would stand there for a bit and then all fly off and then all fly back again. I’d never seen so many congregate in one space like that. It was pretty cool. Maybe they were migrating from the Arctic on their way to points further south.
Arctic Terns are grey and white with a black head and a red bill and short red legs and feet. They are very distinct looking.