Re: I do not know "frigate birds", but the meaning of the name of these birds you wrote sugests that this is right. In portuguese the name of these birds is "gaivotas", the dictionary translation is "seagull".
I don`t agree with my friend Sobreiro, in portuguese these birds are called of "patos ", "gaivota" or seagull are another kind of birds.
Any way they are very beautiful!