The Sandwich Tern has three subspecies: The Sandvicensis breeds on the Atlantic and Mediterranean coasts of Europe, and winters off western Africa and Arabia; the marginally smaller Acuflavida breeds on Atlantic coasts of North America, wintering in the Caribbean and further south, and has wandered to Western Europe;the yellow-billed Eurygnatha breeds on the Atlantic coast of South America from Argentina north to the Caribbean.
Sandwich Terns breed in very dense colonies mostly on coasts and islands. It nests in a ground scrape and lays one to three eggs.
The Sandwich Tern's thin bill is black with a yellow tip, except in the yellow or orange billed South American race. In winter, the Sandwich Tern's forehead becomes white.