Nazca boobies are the largest of the boobies on the Galápagos Islands and have green feet, due to their diet of sardines. Like their blue-footed relatives, they are ground nesters.
Although the birds sit on two eggs, only one chick will survive due to a practice known as ‘siblicides’ (the killing of a sibling, regardless of the food supply). The eggs will hatch around four days apart and the older (or stronger) chick will kick the younger (or weaker) one out of the nest. It is believed that two eggs are laid as an insurance policy; if the older chick’s egg is damaged or the chick dies then the younger sibling will survive.