Juvenile/Second-year Frigatebird, Tainan Taiwan May 2020
I think this is an 'older' juvenile frigatebird as the black breast sides/tabs have not yet been replaced with white. I thought it must be Great Frigatebird in the field due to the shape of the belly patch (large and rounded below the breast tabs) and the absence of white axillary spurs. However, when I look at the photos, there are one or two isolated white feathers on the underwing well forward of the breast patches which should not be there on Great.
I see on average a couple of Lesser Frigatebirds a year, and these are obvious on account of their small and triangular-shaped belly patches (with much less white on the hindflanks) and axillary spurs. As the white belly patch should get smaller (not larger) with age in both sexes (and in both species), I'm not really sure which one this is!