Originally Posted by andyb39
I had always thought that the breast tabs were not remnants of the breast band but evolved independently of it and are in any case positioned slightly lower. I may be wrong. They are in any case still present in 3rd year birds according to the table, so presumably not just a remnant.
Again according to that table, Great has neither axillary spurs nor breast tabs, so should be ruled out. Lesser has no breast tabs and in any case lacks the hulking, heavy-billed shape of your bird.
Yes, I do see what you mean. In view of the rarity of CIF here, though, I was looking for ways to explain how a Great Frigatebird might come to have an underpart pattern like this one, not a CIF. My speculation that the breast band may get 'partially moulted out' and leave a remnant 'tab' is me trying to fit a square peg into a round hole. The more inaccurate this is, the better, as it only strengthens the case for Christmas Island Frigatebird!