A medium to small blue-gray tern endemic to New Zealand. Breeding birds have a black cap extending down to the bill and bright orange bill and legs. Non-breeding plumage dulls to a mottled gray cap and black patch around the eye, also seen in juveniles. Breeds only along the braided rivers of the eastern South Island. Will defend nest from intruders by diving, calling harshly, and hitting intruders on the head. After breeding, populations disperse to coastal areas, foraging offshore and near coastal farmland. A small number will visit the North Island. Call is a repetitive “kit.”