Viewers should be aware that Black Noddy shows broad geographic variation worldwide, with at least one subsp. (Hawaiian erythrogenys) probably deserving species status. So if your experience is entirely with tropical Pacific forms, especially in the main Hawaiian Is., you should identify this bird with caution. My credentials are that I have experience with both species in both oceans, mostly in the Pacific, and took photos of a Black Noddy at Dry Tortugas in March 1991. I have also examined specimens of all forms in several museums. I will address both of the recently reported Blacks in this note. The biggest difference between Black and Brown noddies is in their names. Blacks are always noticeably blacker than Browns, with no dorso/ventral contrast ( except in Hawaii). If it looks brown, it's a Brown. On that basis, both birds looks the same color as the surrounding Browns. Another plumage feature of adults that is important in the Pacific is that the tail is paler than the rest of the plumage. Some references say that Atlantic/Carib birds lack the paler tail, but specimens show the tail to be at least slightly paler. Interestingly, in specimens the tail contrast does not show as well in the hand as in a specimen viewed from a distance. The paleness seems to be the result of a "bloom" on the tail feathers that can rub off in specimen prep and handling. The Black Noddy I photographed in Dry Tortugas a long time ago showed a pale tail, even though its head features were that of a juv with sharply defined white cap. The tail of both recently reported birds is so hard to see that I can't really say much about it. A third plumage feature often overlooked is that Brown Noddies have darker primaries than the rest of the plumage, so that the folded wing shows a sharp contrast between brown secondaries and black primaries. Both recent "Blacks" show a strong primary/secondary contrast. Both birds do, indeed, look a little smaller than surrounding birds, but size is a tricky thing and so-called "runts" appears in many species. Bill thickness and length are often mentioned in ID of the two noddies, and the first bird looks to have a somewhat more slender and maybe proportionally longer bill. The second bird shows what I would consider a typical Brown Noddy bill. For readers using the NGS field guide, note that the images of Black Noddy bills in that book are grotesquely overlong and droopy; totally misleading. I think both recent birds are within the range of variation for bill length in Brown Noddy. Neither of these birds is a Black Noddy.