The Nazca Booby (Sula granti) is a booby found in the eastern Pacific Ocean, primarily on the Galápagos Islands and on Clipperton Island. The Revillagigedo Islands off Baja California may be the northwesternmost limit of its breeding range.

We watched as two teenagers squabbled over whose rock it was.

Taxonomy: The Nazca Booby was formerly regarded as a subspecies of the Masked Booby but is now recognized as a separate species. They differ in regard to ecological and morphological as well as mtDNA cytochrome b sequence data. The Nazca Booby co-occurs with the Masked Booby on Clipperton Island, where they rarely hybridise.

Behaviour: Nazca Boobies are known for practicing obligate siblicide. Mothers lay two eggs, several days apart. If both eggs hatch, the elder chick pushes its sibling out of the nest area, leaving it to die of thirst or cold. The parent booby cannot intervene and the younger chick inevitably dies. Two eggs are laid so that if one gets destroyed or eaten, or the first chick dies soon after hatching, the second egg will produce an offspring.

Adults that have failed to breed frequently seek out nestlings in their colony, and during those visits they often bite, preen and even try to copulate with chicks. The causes of this behaviour are not fully understood, but it is well known that the surviving first chick becomes a natural bully, whereas a surviving second chick (dead first chick) is not.