The Caspian Tern is the largest tern in Australia, with long, slender backswept wings and a slightly forked tail. The heavy bill is red with a dusky tip. When breeding the tern is white, except for a black crown from bill to nape and a short shaggy black crest. The mantle and upperwings are grey and the flight feathers are darker. The eye is dark brown and legs are black. When not breeding, the crown is finely streaked white. The sexes are similar. Immature birds are similar to non-breeding adults. Younger birds are mottled grey and brown.