These gulls started appearing around the lake a couple of weeks ago. I did some research and have identified them as Bonaparte's gulls. They are described online as an unusually graceful, dove-like gull species...one of the smallest gulls in North America. During the breeding season the adult has a black 'hood' covering the face and crown. They mostly breed in wetlands within the boreal forest region of Canada and Alaska...they are most often seen on lakes and rivers during migration or along the coast in winter.