Thalasseus

Thalasseus, the crested terns, is a genus of eight species of medium-large to large terns in the family Laridae.

The species have a worldwide distribution in temperate and tropical seas, mostly between about 43° N and S latitude, but to 60° N in the warm waters of the North Atlantic Current in the eastern North Atlantic Ocean. They do not occur in colder arctic or antarctic waters. Several of the species are abundant and well-known birds in their ranges; one is however extremely rare and critically endangered. This genus had originally been distinguished by Friedrich Boie in 1822, but had been little used (with one exception in 1978) until a 2005 study confirmed the need for a separate genus for the crested terns.