Sterna

Sterna is a genus of terns in the bird family Laridae. The genus used to encompass most "white" terns indiscriminately, but mtDNA sequence comparisons have determined that this arrangement was paraphyletic. It is now restricted to the typical medium-sized white terns with deeply forked tails, which occur near-globally, mostly in coastal regions but several also using freshwater habitats inland. (Wikipedia)