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
Tern another by call, and siblings also recognise each other's vocalisations from about the twelfth day after hatching, which helps to keep the brood together. Vocal differences reinforce species separation between closely related birds such as the least and little terns, and can help humans distinguish similar species, such as common and Arctic terns, since flight calls are unique to each species. Terns have a worldwide distribution, breeding on all continents including Antarctica. The northernmost and southernmost breeders are the Arctic tern and Antarctic tern respectively. Many terns breeding in temperate zones are long-distance migrants, and the Arctic tern probably sees