Taxonomy
The terns, family Sternidae, are small to medium-sized seabirds closely related to the gulls, skimmers and skuas. They are gull-like in appearance, but typically have a lighter build, long pointed wings (which give them a fast, buoyant flight), a deeply forked tail and short legs. Most species are grey above and white below, and have a black cap which is reduced or flecked with white in the winter.
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| Relationships in the genus Thalasseus |
The Greater Crested Tern was originally described as Sterna bergii by German naturalist Martin Lichtenstein in 1823, but was moved to its current genus, Thalasseus, after mitochondrial DNA studies confirmed that the three main head patterns shown by terns (no black cap, black cap, black cap with a white forehead) corresponded to distinct clades.
The Greater Crested Tern's closest relatives within its genus appear to be the Lesser Crested Tern (T. bengalensis), and the Royal Tern, (T. maximus). The DNA study did not include the critically endangered Chinese Crested Tern (T. bernsteini), but as that bird was formerly considered to be conspecific with the Greater Crested Tern as a synonym of the subspecies T. b. cristatus, it is presumably also very closely related.
The genus name of the Greater Crested Tern is derived from Greek Thalassa, "sea", and the species epithet bergii commemorates Carl Heinrich Bergius, a Prussian pharmacist and botanist who collected the first specimens of this tern near Cape Town.
The Greater Crested Tern has about five geographical races, differing mainly in the colour of the upperparts and bill. These are listed below in taxonomic sequence. A similar number of other potential subspecies have been proposed, but are not considered valid.
| Subspecies | Breeding range | Distinctive features | Population estimates |
|---|---|---|---|
| T. b. bergii (Lichtenstein, 1823) |
Coasts of South Africa and Namibia | Dark grey above, slightly larger than thalassina, least white on head | 20,000 individuals (inc 6,336 breeding pairs in South Africa and up to 1,682 pairs in Namibia) |
| T. b. enigma (Clancey, 1979) |
Zambezi delta, Mozambique, south to Durban, South Africa | Palest subspecies | 8,000–10,000 individuals in Madagascar and Mozambique |
| T. b. cristata (Stephens, 1826) |
Eastern Indian Ocean, Australia and western Pacific Ocean | Like bergii, with tail, rump and back concolorous. paler in Australia | 500,000+ individuals in Australia |
| T. b. thalassina (Stresemann, 1914) |
Western Indian Ocean | Small and pale, larger and less pale in south of range | 2,550–4,500 individuals in Eastern Africa and Seychelles |
| T. b. velox (Cretzschmar, 1827) |
Red Sea, Persian Gulf, northern Indian Ocean | Largest, heaviest, darkest and longest-billed subspecies | 33,000 in Middle East (inc 4,000 pairs Oman and 3,500 pairs on islands off Saudi Arabia) |
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