Nazca Booby Birds are the largest of all the boobie birds on the Galapagos Islands.
Nazca Booby Birds lay two eggs, several days apart from which only one chick survives due to a practice called ‘obligatory sibling murdering’. In this process, one of the chicks displaces the other by taking most of the food, therefore growing faster. Once that has been achieved, the larger chick kicks the smallest and weakest chick out of the nest, leaving it to die of thirst or cold. The parent Nazca Booby Birds will not intervene and the younger chick will inevitably die.
It is believed that two eggs are laid so that one remains an insurance in case the other gets destroyed or eaten e.g. by gulls, or the chick dies soon after hatching.