Bill-length as a field-character of the White-winged Black Tern ? In his paper on 'Juvenile and winter plumages of the marsh terns' (Brit. Birds, 53: 243-252) Kenneth Williamson differentiated without qualification between the bill of the Black Tern Chlidonias niger as 'long, slender and looking slightly decurved' and that of the White-winged Black Tern C. leucopterus as 'short and stubby' (p. 249) and ...

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