To me, the Klingon Bird of Prey was inspired by the earlier Romulan one, or perhaps a later model. In TOS, the Romulans were using the Klingon D7 in "The Enterprise Incident," which kind of implied that the Klingons and Romulans were briefly allied against the Federation for awhile and shared some spacecraft ideas during that time, IMO. It would sort of explain (in-universe) why ship terms such as "bird of prey" and "warbird" have been used by both the Klingons and the Romulans in their history.