 The greater crested tern is a large tern with a long ( 5 @.@ 4 – 6 @.@ 5 cm or 2 @.@ 1 – 2 @.@ 6 in ) yellow bill , black legs , and a glossy black crest that is noticeably shaggy at its rear . The breeding adult of the nominate subspecies T. b. bergii is 46 – 49 cm ( 18 – 19 @.@ 5 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 . 
