The Arctic tern (Sterna paradisaea) is a tern in the family Laridae. These amazing birds perform the longest migrations known in the animal world. They have a circumpolar breeding distribution and see two summers each year. Arctic terns nest once every one to three years and they are long-lived birds, with many reaching up to 30 years of age.
The Arctic tern is a small seabird with short legs and comparably narrow wings. The beak is dark red, as are the short legs and webbed feet. Like most terns, the Arctic tern has high aspect ratio wings and a tail with a deep fork. The adult plumage is grey above, with a black nape and crown and white cheeks. The upperwings are pale grey, with the area near the wingtip being translucent. The tail is white, and the underparts are pale grey. Both sexes are similar in appearance. The winter plumage is similar, but the crown is whiter and the bills are darker. Juveniles differ from adults in their black bill and legs, "scaly" appearing wings, and mantle with dark feather tips, dark carpal wing bar, and short tail streamers. During their first summer, juveniles also have a whiter forecrown.
Habitat of the Arctic tern covers a huge territory, extending from arctic and sub-arctic regions of North America, Europe, and Asia to coastal regions with mild temperatures in summers, reaching as south as Brittany and Massachusetts. Within regions of their habitat, Arctic terns are met anywhere from seacoasts to lakes and swamps. As summer approaches in the Southern Hemisphere, terns migrate right up to the Antarctic Ice.
Terns are very communicative and sociable animals: every year they congregate for nesting in the same place, making up large groups. They fiercely defend the nesting area, building the nests close to each other. These birds see the most sun due to the fact that they migrate from the Arctic summer to Antarctica, thus living in constant summer. Arctic terns are diurnal, meaning that they are active during the day. When they search for food, they fly upward for a while and then hover in the air, looking carefully for prey on the water’s surface. During their long-distance migrations, Arctic terns stop to rest right on the water or on floating logs.
Arctic terns are carnivores (piscivores).These birds feed upon small species of fish (sand launaes, sand eels, and capelins) as well as crayfish.
Arctic terns are monogamous, meaning that they mate once in a lifetime. Migrating there and back, they usually camp in the same places every year. The mating ritual looks as follows: a male performs so-called “fish flight”, carrying caught fish through the air, accompanying the process with screaming sounds (they are able to shout with prey in their mouths), after which it lands and offers the prey to the female. Their nesting areas are rocky or sandy beaches of the far north, where the birds congregate in colonies. Before incubation, Arctic terns excavate hollows in grit or sand. Incubation takes place in summer, from June to July, lasting about 21-22 days. The female typically lays 2-3 eggs. When hatched, the chicks are downy. Neither altricial nor precocial, they begin to move around and explore their surroundings within one to three days after hatching. Usually, they do not stray far from the nest. The chicks are protected and cared by both parents during the first 10 days of their lives. After another 10-15 days they are able to fly. Both males and females of arctic terns start breeding at 3-4 years old.
Threats to Arctic terns’ population are many: rats and hedgehogs, attacking their nests; enlargement of human habitat; disturbance of terns in their home range by entertainment purposes; excessive fishing by humans, led to lack of sand eels, the major source of food for Arctic terns. In addition, changes, now taking place in Arctic and Antarctic ecosystems, will definitely affect Arctic terns.
The total population of Arctic tern is officially estimated by IUCN, counting up to 2 million individuals. Thus, only 10.000-100.000 breeding pairs and 1.000-10 migrating individuals have been estimated in Russia. The population as a whole isn’t endangered, being listed in the IUCN Red List as of Least Concern (LC) with a decreasing population trend.
Being sea predators, these birds noticeably control the marine ecosystem in their habitat. They influence the population number of species they feed on. Sometimes they catch and leave the prey, giving opportunity local scavengers to take advantage of it. And finally, Arctic terns serve as the major source of food for many animal species in the area.
