Charrán Ventrinegro Sterna acuticauda

Elegant tern with a long tail and a slender orange bill. Breeding adult has a full black cap and dark belly. Non-breeding adult is paler-bellied and has only a solid black nape patch, with the black of the crown reduced to mottling. Larger, bulkier River Tern can be similar, but averages shorter- and thicker-billed, lacks black belly in breeding plumage, and has patchier black on the head in non-breeding plumage. Black-bellied breeds on sandy or gravel islands in rivers and lakes, but forages over a wider range of wetland habitats. Gives squeaky “wee’tew!” notes. Uncommon and declining.