Description

This species is particularly attracted to the lights of ships at night and hundreds have been known to continuously circle lighted ships raucously calling and often landing on the decks in large numbers.

Identification Guide: With good views, adults should not be confused with the other dark and white tern in BIOT, Bridled Tern being a warm brown colour whilst Sooty Tern is a sooty-black colour. Juveniles are separable on general colour, young Bridled Terns are much lighter coloured and have paler crowns, while juvenile Sooty Terns are dull sooty-black above and below with variable white or beige spots on the upperparts. Juveniles of these species are unlikely to be encountered on the same islands and Bridled is seldom found far away from land. The most likely area where the two species will be seen together is around Resurgent, where a small number of breeding Bridled Tern are sandwiched between Sooty Tern colonies on South and Middle Brother.

Status and Distribution: Not a common species throughout the Territory, except on islands where it breeds in dense colonies. Sooty Tern has been impacted catastrophically as a breeding species by the presence of man and his commensals, particularly on Diego Garcia. For example, the breeding population on Diego Garcia was estimated in the order of 100,000 pairs in July 1884 and shortly after was thought to have completely ceased breeding on this atoll. Since 1996, breeding has been recorded on Danger Island, Sea Cow, the Three Brothers, and, in Peros Banhos, Parasol, Longue, Petite and Grand Coquillage and Petie Ile Bois Mangue. In February 1996, 73,000 breeding pairs were found throughout the Territory; in 2006, a total of 82,208 pairs were found. The breeding phenology of this species in BIOT is not understood. It has been recorded breeding throughout the year and does not nest on all islands where it is known to breed in any given year. Therefore, an accurate figure for the total breeding population in the Territory cannot yet be given. Away from the breeding islands, it is only occasionally seen and is by no means common. On Diego Garcia, it is more often heard flying over at night calling than seen off the shore.