Blue-footed booby
The blue-footed booby is a specialized fish eater, feeding on small schooling fish such as sardines, anchovies, mackerel, and flying fish. It will also take squid and offal. The blue-footed booby hunts by diving into the ocean after prey, sometimes from a great height, and can also swim underwater in pursuit of its prey. It can hunt singly, in pairs, or in larger flocks. Boobies travel in parties of about 12 to areas of water with large schools of small fish. When the lead bird sees a fish shoal in the water, it will signal to the rest of the group and they will all dive in unison, pointing their bodies down like arrows.
Blue-footed booby
Food problems may be the cause of an observed failure of the birds to even try to breed. The results of the research suggest this is related to a decline in sardines ("Sardinops sagax"), an important part of the boobies’ diet. Earlier work on Española Island saw successful breeding in blue-footed boobies that have access to sardines, in which case their diet consists essentially wholly of sardines. However, sardines have been largely absent from the Española area since 1997, as has been shown from Nazca boobies there, who also prefer sardines but can breed using other prey. In 2012–13, roughly only half of prey items in the boobies' diet were sardines. No evidence was seen of other possible causes for the decline, such as effects of humans, introduced predators, or disease.