The White tern is a very elegant and delicate seabird, with immaculate all-white plumage. The small eyes surrounded by black rings make them seem much larger. Adults look the same, but juveniles have a brownish-gray back and gray on their neck, with a black mark behind their eye. These dainty terns fly in an undulating pattern with deep, slow wingbeats, which, although it appears erratic, is very strong and enables sustained periods of hovering.
White terns breed in subtropical and tropical South Atlantic, Pacific and Indian Oceans. They are a pelagic bird that lives in oceanic areas, relatively close to coral breeding islands with some vegetation, where it will nest in bushes and trees, foraging over deep ocean waters.
White terns are often seen on their own or in small groups. They are a diurnal species, but are more active at dawn and dusk. To eat, it dips its beak to catch prey at the water’s surface or just beneath it. A dive is often preceded by extensive hovering, and the bird may use the wind to sustain its flight. It may catch flying fish from the air, and it is commonly seen foraging near groups of predatory fish and dolphins which drive their prey towards the surface. An individual may carry a few small fish in its bill, taking these to its young with the prey held crosswise. If disturbed by a predator, a White tern will hover, flutter and make buzzing sounds. This bird has a graceful flight. It flies easily low above the waves, without landing. It will touch the surface once it has spotted prey. Its flight is buoyant, involving erratic changes in speed and direction.
White terns are monogamous and pairs remain with each other for several seasons, returning every year to the same nesting site. These birds nest in loose groups or singly. They can breed at any time during the year, but there are peaks from late spring until early summer. At the start of the breeding season, pairs engage in aerial displays, flying with each other. They probably do courtship feeding, with the male giving some prey to his mate, and mutual preening while perched on a branch. These birds do not build a nest. Sometimes they will scratch the bark of a short branch high in a tree, to make a small shallow depression, using their feet and bill to do so. The egg is sometimes laid on a roof or other surface, but always on a bare surface. One speckled egg is laid and incubation is for about 36 days, by both parents. The chick is brooded in its branch nest. Both parents feed their chick every 3 hours, bringing small fish or squid. The young fledges at around 48 days of age, when it moves into the area surrounding the nest site. It returns to the nest branch only for feeding. Both parents feed it for 2 more months. Young reach maturity at around 3 to 5 years.
Although currently not at risk of extinction, White terns are threatened by predation from cats and rats, introduced onto some of their breeding islands. This has caused some populations to decline and others have disappeared.
According to the What Bird resource, the global White tern population size is around 160,000 to 1,100,000 individuals. The Hawaii Comprehensive Wildlife Conservation resource records the total population in the Hawaiian Archipelago of the White tern as 15,000 breeding pairs, with the largest populations being on Midway (7,500 pairs), Laysan (1,000 pairs) and Nihoa (5,000 pairs). On O‘ahu Island between 1961 and 2005, pairs increased from one to more than 250. The worldwide population probably exceeds 100,000 breeding pairs. Overall, currently White terns are classified as Least Concern (LC) on the IUCN Red List and their numbers today remain stable.