In "Balance Of Terror" Stiles says that Romulan ships are painted like giant birds of prey (or something to that effect. Hence, the term stuck even though neither the Federation or the Romulans refered to the ships that way. Note that in some novels some writers made references that the Romulans thought of their ships that way, and why not(?), because they consciously did paint their ships that way.
TNG's Romulan ships were actually more consistent with this idea than TSFS. But by then the damage was done.