This is a male frigatebird in flight, viewed from the rear. I can’t ID the exact species from this picture, because the best way to do that is look at the color of the feathers. But I can tell it’s male because you can see the red gular sac located at the throat–that’s the red bump hanging down below the body. Gular sacs are very prominent in male frigatebirds and are used for courtship displays.
As you can see, this cliff area of Genovesa, or Tower, island is swarming with sea birds: frigatebirds, boobies, petrels, etc. They nest on the cliffs and feed in the waters by swooping down. Frigatebirds are sometimes called “pirate” or “Man o’ war” birds because they have a habit of stealing other birds’ catches.