This is a medium-large tern, 37-43 cm (15-17 in) long with an 85-97 cm (33-38 in) wingspan. The Sandwich Tern's thin sharp bill is black with a yellow tip, except in the yellow or orange billed South American race. Its short legs are black. Its upperwings are pale grey and its underparts white. This tern looks very pale in flight, although these flight feathers darken during the summer. The Lesser Crested Tern and Elegant Tern differ in having all-orange bills. Lesser Crested also differs in having a grey rump and stouter bill, and Elegant in having a slightly longer, slenderer bill. Chinese Crested Tern is the most similar to Sandwich, but has a reversal of the bill colour.
The Sandwich tern feeds by plunge diving for fish, usually in marine environments.
It nests in a ground scrape and lays one to three eggs.
Calls and Songs
The Sandwich Tern is a vocal bird; its call is a characteristic loud grating kear-ik or kerr ink.