Nazca boobies in the Malpelo Island consume mainly one species of fish, Oxyporhamphus micropterus, from the family Hemirhamphidae. The second most significant family in their diet is Exocoetidae (flying fish), followed by Carangidae (jacks and pompanos) and Scombridae (tuna). Although, O. micropterus is consumed with a higher frequency, flying fish make the highest weight contribution to the Nazca booby’s diet in Malpelo. Other families of small fish are consumed exclusively by males. In this colony squids represent less than one percent of the diet of these birds (García & López-Victoria, 2007) .
This contrasts with the diet of boobies in the Galápagos islands where anchovies (Engraulidae) and sardines (Clupeidae) make up a significant part of the birds’ nutrition. Additionally, the Nazca boobies in Galápagos do not consume squid and only consume hemirhamphids and scombrids in a reduced proportion. Flying fish as the dominating item of the boobies’ diet is the only conserved dietary similarity between the colonies in the Galápagos and in Malpelo. Secondary components of the diet may vary due to the distribution of fish species around the islands, depending on the oceanographic currents that pass through each area (García & López-Victoria, 2007).
There are reported differences in the diet of males and females of the Malpelo colony. Females consume more food than males in general and in proportion to their body weight (García & López-Victoria, 2008). Furthermore, females have a slight preference for larger prey, while males prefer smaller prey (belonging to different fish families) (García & López-Victoria, 2008). This could be correlated with the sexual dimorphism in body size exhibited by this species. However, the differences in prey size between males and females could also reflect differences in the foraging sites and foraging behavior or result as a response to intraspecific competition for food resources (García & López-Victoria, 2008).