Altho rare on Atlantic coast I have seen a few among Common Terns down on the Carolina shore near Ocracoke Inlet. Their harsh grating notes are the best identification and black patch on side of young birds' heads helps in separation. A hundred or more Common Terns, with a few of this species, were fishing in the Inlet, catching small silvery fish with every swoop. Their accuracy of aim and swift strike were remarkable — they seldom missed, sometimes securing two at a time.
From Oregon, east to Manitoba, south thru northern Illinois, Nebraska and Colorado to coasts of Gulf States. Rare on Atlantic coast as far north as Massachusetts.