The Royal TernThalasseus maximus during breeding season has a black crown and an orange bill without the black tip seen in the Forster’s tern. Its bill is thinner than that of the Caspian Tern. During non-breeding season the crown is whitish over the forehead. These photos were taken at the salt marshes at Cape May in early October.
Unlike Forester’s Tern that looks like it is wearing a black mask, in the non-breeding phase the black is swept to the back of the head.