Forester's Tern: larger body size than the Least Tern. The Forester’s Tern has orange legs and bill and lacks the white forehead patch of the Least Tern. The Forester’s Tern also has a pale gray tail with white outer margins which differs from the Least Tern.
Common Tern: larger body size than the Least Tern and lacks the white forehead patch. Very closely resembles the Forester’s with orange legs and bill and a completely black cap. The Common Tern has darker primaries than the Forester’s Tern and its tail is white with pale gray outer margins.
Black Tern: the winter plumage of the black tern closely resembles the winter plumage of the Least Tern. The Black Tern is slightly larger than the Least Tern with darker gray wings and tail and darker legs.