Hi Chris (x2), John, Philip & Ed,
I agree with John & Chris that the birds look like 1st winter White-winged Terns.
And yes, Ed is right, both IOC and Clements call them White-winged Tern.
However, the old name was White-winged Black Tern (no hyphen), which is likely a more descriptive name and not a classifier for a group (Chlidonias doesn’t stand for ‘Black-Tern’; it rather stands for ‘Marsh-Tern’). This is in contrast to the hyphenated birds that Philip mentioned, which all classified a group: Black-Cockatoo is used only for Calyptorhynchus, Bronze-Cuckoo stands for Australian Chrysococcyx (with Black-eared Cuckoo being the exception), Reed-Warbler describes a number of Acrocephalus.
Nikolas
