Trinidad and Tobago Field Naturalists' Club         Southeastern Caribbean Bird Alert         Trinidad and Tobago Rare Bird Committee
Sandwich Tern (Sterna sandvicensis acuflavida) and Cayenne Tern (S. s. eurygnatha): Page 6 of 7
Page 1: Virgin Islands (variability)
Page 2: Virgin Islands (hybridisation)
Page 3: Aruba (hybridisation)
Page 4: Tobago
Page 5: Brazil
     Page 6: Argentina
Page 7: Argentina
    The following five photographs, © by Flavio Quintana and Yorio Pablo, were taken at Punta León, Chubut, Argentina, in November 2000.
Cayenne Terns in a mixed colony of Royal Terns (S. maxima). Note the relatively short-billed bird near centre.
Note the orange-tinged base of bill on tern at upper left and slight dusky tinge on bill at bottom. Note also the plain grey primaries and pure white rectrices.
Note the dark markings on the bill of several terns. A Kelp Gull (Larus dominicanus) is at left-centre and a Royal Tern at lower right.
Note the variability in bill shape, with a distinctly downward-curving bill at left-centre, a fairly straight bill at right-centre, and a short, stout bill at bottom right. Also note the orange-tinged base of bill at lower left.
Note the extensive dark blotches on bill of bird at top right. Such birds in the southern Caribbean colonies were initially thought to represent hybrids between Cayenne Tern of South America and Sandwich Tern (S. s. acuflavida) of North America, but given the presence of such 'intermediate' bill types among presumably 'pure' Cayenne Terns in southern South America, hybridisation or introgression seems unlikely.