Firth of Clyde, Scotland.
In some respects intermediate between Sterna and Thalasseus. Genetic data#R indicate that present species, S. hirundinacea, S. hirundo, S. paradisaea and S. vittata may form a monophyletic group that also includes Old World S. striata and S. sumatrana, with S. forsteri and S. trudeaui possibly also part of this group. May hybridize with S. hirundo and S. paradisaea. Internal taxonomy in need of revision, as subspecific boundaries confused: racial allocation of birds breeding on islets off E Africa requires study, perhaps closer to bangsi than to nominate dougallii, although included in latter; arideensis may not be distinct from bangsi; variation of nominate encompasses almost entire range of variation of the species. Has been suggested that arideensis, korustes and bangsi be synonymized with gracilis#R. Five subspecies currently recognized.
Food and feeding
Status and conservation
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