Calling the Romulan ship a bird of prey is the correct term for TOS era Star Trek. They were called that in several episodes (most notably in "Balance of Terror). In canon, the Klingons picked up the term bird of prey after an alliance with the Romulans which altered the designs of their ships. The warbird designation came about when the producers needed a name for the bigger warships the Romulans used in TNG.

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