Frigatebirds

From this close-up of the female frigatebird, you can see that they are not so dull in appearance as first looks suggest. She has a interesting combination of a blueish beak and golden head feathers along with ghostly white feet.

When in flight, the male really dominate the sky.

While the nearest bird in flight dominate this image, you'll notice that there are two other males in flight farther away and a female perched on her nest in the bushes. It is surprising how close to the ground these birds build their nests. 

While cats and rats are among their predators, I suspect this island is well protected from these menaces but controlling the access carefully. However, frigatebirds are known to push the eggs out of other frigatebird's nest.