Know Before You Go

Terns are closely related to gulls, and some experts consider the two groups as one family. But whereas gulls often soar in wind currents and up-draughts, terns fly in straighter, more level paths. The majority of terns are coastal seabirds, but two species, the Arctic tern and the Antarctic tern, migrate annually over open ocean.

The Arctic tern has the world’s longest migration route of any animal, flying 44,000 miles in a zigzagging formation from its breeding grounds in Greenland to Antarctica. The Antarctic tern, by contrast, travels far less, staying all year in ice-free waters in the Antarctic.

The Arctic and Antarctic terns are very similar, both in appearance and habits. Their diet consists primarily of fish, which they snatch from the water by swooping down after hovering at the surface. Terns can dive short distances for their prey if needed. They breed at opposite ends of the Earth at opposite seasons, so the Arctic species will be in winter plumage when it visits in the Antarctic summer.

Most terns nest in colonies, but the Antarctic tern often nests on its own or at best in loose and widely segregated breeding areas. The male and female take turns incubating the eggs, which are between one and three in number. After three weeks, the chicks hatch, and parents share the duties of feeding and caring for their young.

Nests are constructed by scraping an indention in loose pebbles. At 4 or 5 weeks old, the birds fledge, but parents will continue fishing for their young past this time. The eggs and young are well camouflaged against the gray pebbles, and a visitor can easily wander too close without realizing it. However, Antarctic terns will soon warn any potential trespasser by diving and scolding. If this happens, the visitor should retreat, whereupon the terns will resume sitting on their eggs or brooding their chicks.Header Credit: Moira Le Patourel