Terns are the sea birds which belong to family Sternidae. Previously they were considered a subfamily Sterninae under gull family Laridae. Terns are related to gulls and skimmers, which in turn are related to skuas and auks. Terns can be found worldwide.
Most of the tern species were previously placed into one large genus Sterna and the other small genera. But after the analysis of DNA sequences Sterna genera is split into several smaller genera.
Most of the tern birds, those who breeds in temperate zones are the long-distance migrants. Arctic Tern sees more daylight as it migrates from its northern breeding lands to Antarctic waters. One Arctic Tern take off from Northumberland coast in eastern Great Britain in summers 1982 and reached in October 1982 at Melbourne, Australia is recorded as one of the longest journey ever by a bird. It has traveled 22,000 km distance in just three months, traveling over 240 km per day.
Terns are medium to large in size. They have grey or white plumage with black markings on the head. They have somewhat long bills are with webbed feet. Terns have long narrow wings with long tails. Terns which belong to genus Sterna have deeply forked tails, while the noddies have notched wedge shaped tails. The size of terns ranges from 42 g (1.5 oz) and 23 cm (9 inches) to 630 g (1.4 lbs) and 53 cm (21 inches). Terns make harsh, single-note sounds.
Many terns catch their fish by diving into water, while some lives on eating the insects from the water surface. Terns glide rarely, however some species especially Sooty Tern can soar high. Excluding bathing, terns rarely swim, despite having webbed feet.
Terns are colonial birds, live in large, densely packed colonies. Some species build their nests on ground while some nest on trees. Terns are one of the long-lived birds. Many of its species are living in excess of 25-30 years.