ハシグロクロハラアジサシ Chlidonias niger

Small tern with an entirely black body in breeding plumage with silvery wings. In the winter, their body is whitish-gray and they are not as conspicuous, but note small size, rather dark gray wings and rump, and black "helmet." Breeds in colonies in freshwater marshes and ponds. Builds a floating nest of plant matter. In migration and winter, often found in flocks. Feeds on insects and small fish.