Tern make up the clutch. Most species feed on fish caught by diving from flight, but the marsh terns are insect-eaters, and some large terns will supplement their diet with small land vertebrates. Many terns are long-distance migrants, and the Arctic tern may see more daylight in a year than any other animal. Terns are long-lived birds and are relatively free from natural predators and parasites; most species are declining in numbers due directly or indirectly to human activities, including habitat loss, pollution, disturbance, and predation by introduced mammals. The Chinese crested tern is in a critical situation and three other
Royal tern adult royal tern has an average wingspan of , for both sexes, but their wingspan can range from . The royal tern's length ranges from and their average weight is anywhere from . The calls of the royal tern are usually short, clear shrills. Some of the shrills sound like "kree" or "tsirr"; the royal tern also has a more plover like whistle that is longer, rolling and is more melodious. In various parts of its range, the royal tern could be confused with the elegant tern, lesser crested tern (the other orange-billed terns), and the greater crested tern. It