Also, I'd say the phrase "warbird" might be a synonym for "bird of prey" to both Romulans and Klingons.
Actually, since those terms are used in parallel, and never for the same ship class, I'd suggest there's a very definite difference between them - just like there's a difference between "destroyer" and "cruiser".
Birds of Prey might be at the smaller end of the ship spectrum for any given era, while Warbirds are the absolute top predators. And Raptors could be small torpedo boats with even more limited capabilities than those of a Bird of Prey. This would hold for all eras of Klingon warship design, and for all eras of Romulan warship design, although of course a Warbird from the 22nd century would probably be smaller and weaker than a Bird of Prey from the 24th, and a Romulan Warbird might be stronger or weaker than her Klingon equivalent at any given time. But the choice of terminology would depend on the speaker, and the listener, and the interpreter...
(A Soviet skipper from the 1970s would not have spoken of "destroyers" in his native language, but an interpreter might have turned the word he used into English in several ways: "squadronship" if he insisted on perverting the guy's words into the literal translation of the pre-Soviet term for destroyer, "destroyer" if he insisted on perverting the guy's words into the NATO equivalent for the vessel type, and "large ASW ship" if he agreed to a truly literal translation. The English listener would choose what he wants to hear based on his profession and background, too.)