[order] Charadriiformes | [family] Sternidae | [latin] Sterna fuscata | [UK] Sooty Tern | [FR] Sterne fuligineuse | [DE] Russseeschwalbe | [ES] Charrán Sombrío | [IT] Rondine di mare oscura | [NL] Bonte Stern

Bonte Stern determination

copyright: Josep del Hoyo

The Sooty Tern is a distinctively marked, medium-sized tern. Whilst breeding, the plumage of both sexes is black above and white to pale grey on the belly, the outer edges of the wing and the deeply, forked tail. The crown, eyes, bill, legs, feet are black and the forehead is white. In non-breeding plumage, the crown has white streaks and the mantle has white scallops. The juvenile has a “sooty” head, chest and upper parts, a paler grey belly, and the mantle and upper wings are spotted with white.

The Sooty Tern is a pelagic species that forages offshore. Individuals are usually only observed onshore during breeding season or when they have been forced there by stormy weather. In the breeding season, colonies of the species nest on coral cays, atolls, sandbanks, rock stacks, cliffs or other offshore islets. Individuals nest in large colonies often in association with Common Noddies. Nests are generally simple, unlined scrapes or depressions on sand, shingle, rock or grass either in the open, in grassy areas, or under tussocks or bushes.

The Sooty Tern has been observed within the tropical and subtropical waters and islands of the Indian, Pacific and Atlantic Oceans.

The Sooty Tern can be active during the day and night mainly feeding on fish and other small (2-8cm) aquatic animals taken from near the ocean surface. Food may also be scavenged from aerial pursuits of other birds and by hawking for cicadas over forest. The Sooty Tern is carnivorous, feeding on squid, crustaceans, fish and hydrozoans. Individuals have been observed feeding in association with tuna that chase suitable prey close to the surface of the ocean. During nonbreeding periods, flocks of Sooty Terns follow large schools of migratory tuna. However, in the breeding season, the species forages close to breeding islands in association with smaller species of tuna.

This species has a large range, with an estimated global Extent of Occurrence of 1,000,000-10,000,000 km². It has a large global population estimated to be 21,000,000-22,000,000 individuals (Wetlands International 2002). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern. [conservation status from birdlife.org]

Highly ritualized and vocal aerial displays are conducted over nesting area prior to settling down to lay eggs. Nesting locations change slightly from season to season. Breeding occurs in small to large colonies, often mixed with other seabirds. The locality may determine the time of breeding and the breeding cycle. No nest is prepared. Populations have been recorded breeding every twelve months, every nine and a half months and every six months. During spring a single egg is laid, which is then incubated by both adults for a period of 28 days. Young stay in colonies for up to 70 days and then probably accompany their parents at sea for several months. Breeding success rates may be low and breeding age is thought to be 4-5 years.
Heat stress may cause terns to abandon eggs for short periods to drink seawater. Sooty terns are easily disturbed by human activity, and repeated disturbance may result in permanent abandonment.
Chicks are shaded by parents during hot hours and brooded only when cool. Chicks are fed every 16 hours with regurgitated food. Parents locate chicks through vocalizations, and will feed only their own. Fledging occurs at about eight weeks. Offspring continue to be fed by parents for several weeks after fledging.

Rarely seen on water and believed to sleep on the wing. Once chicks fledge (or die), all birds leave colonies. Adults return after 2-3 months at sea, and settle only at night for 2-3 months prior to initiating new breeding cycle. Adults from West Indies disperse into Gulf of Mexico and Caribbean where some winter. Juveniles across Atlantic and moves South down African coast. Little information on Indian Ocean population, which probably disperse widely over Indian Ocean. Pacific adults disperse away from colony June-October and begin to return to area in late November, occupying colony in February, but not laying until April.