In the wintering regions, there are also confusion species, including the Antarctic tern of the southern oceans, the South American tern, the Australasian white-fronted tern and the white-cheeked tern of the Indian Ocean. Identification may be aided by the plumage differences due to "opposite" breeding seasons. The Antarctic tern is more sturdy than the common, with a heavier bill. In breeding condition, its dusky underparts and full black cap outline a white cheek stripe. In non-breeding plumages, it lacks, or has only an indistinct, carpal bar, and young birds show dark bars on the tertials, obvious on the closed wing and in flight. The South American tern is larger than the common, with a larger, more curved red bill, and has a smoother, more extensive black cap in non-breeding plumage. Like Antarctic, it lacks a strong carpal bar in non-breeding plumages, and it also shares the distinctive barring of the tertials in young birds. The white-fronted tern has a white forehead in breeding plumage, a heavier bill, and in non-breeding plumage is paler below than the common, with white underwings. The white-cheeked tern is smaller, has uniform grey upperparts, and in breeding plumage is darker above with whiter cheeks.