Description
The Greater Crested Tern is a large tern with a long (5.4–6.5 cm, 2.1–2.6 in) yellow bill, black legs, and a glossy black crest which is noticeably shaggy at its rear. The breeding adult of the nominate subspecies T. b. bergii is 46–49 cm (18–19 in) long, with a 125–130 cm (49–51 in) wing-span; this subspecies weighs 325–397 g (11.4–14.0 oz). The forehead and the underparts are white, the back and inner wings are dusky-grey. In winter, the upperparts plumage wears to a paler grey, and the crown of the head becomes white, merging at the rear into a peppered black crest and mask.
The adults of both sexes are identical in appearance, but juvenile birds are distinctive, with a head pattern like the winter adult, and upperparts strongly patterned in grey, brown, and white; the closed wings appear to have dark bars. After moulting, the young terns resemble the adult, but still have a variegated wing pattern with a dark bar on the inner flight feathers.
The northern subspecies T. b. velox and T. b. thalassina are in breeding plumage from May to September or October, whereas the relevant period for the two southern African races is from December to April. For T. b. cristata, the moult timing depends on location; birds from Australia and Oceania are in breeding plumage from September to about April, but those in Thailand, China and Sulawesi have this appearance from February to June or July.
The Royal Tern is similar in size to this species, but has a heavier build, broader wings, a paler back and a blunter, more orange bill. The Greater Crested often associates with the Lesser Crested Tern, but is 25% larger than the latter, with a proportionately longer bill, longer and heavier head, and bulkier body. Lesser Crested Tern has an orange-tinted bill, and in immature plumage it is much less variegated than Greater Crested.
The Greater Crested Tern is highly vocal, especially at its breeding grounds. The territorial advertising call is a loud, raucous, crow-like kerrak. Other calls include a korrkorrkorr given at the nest by anxious or excited birds, and a hard wep wep in flight.
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