Thanks,
There is a large colony, several hundred, of Common Terns nesting there and it has attracted a few terns of other species, including Gull-billed, Least, Royal, Arctic, and Sandwich (photographed). I have failed to spot any of them but did see this Roseate 23 days earlier, on June. 6. I was confused by the plumage of the later one.
Roseate Tern
I now see how similar they are, except for the molting.