Feeding in the near-shore waters surrounding oceanic islands, or along the coasts of Central and South America, the Nazca booby can be seen making dramatic plunge dives from heights of up to 30 metres into schools of fish (3) (5) (6). Populations on the Galapagos mostly favour schools of sardines, but during El Niño years, when these fish are scarce, the birds will instead prey on flying fish (3).
The Nazca booby breeds at different times throughout the year according to the location of the nesting colony (2). A minimal nest is constructed with a few small pebbles laid on the ground, in which two eggs are laid a few days apart (6). Interestingly, incubation involves the parent bird wrapping both its feet around the sides and top of the eggs, transferring heat from the dense network of blood vessels in the webbing between the digits (7). Nazca booby chicks engage in siblicide, a behaviour in which the first chick to hatch after the 40-day incubation period invariably attacks the second chick and pushes it out of the nest (6) (8). The parent birds ignore this battle and leave the second chick to die of starvation, or as a result of having its wounds pecked by blood-feeding birds such as mockingbirds and the large cactus-finch (Geospiza conirostris). The reason for such seemingly unnecessarily destructive behaviour is suggested to be because the second egg’s only purpose is to act as insurance in case the first egg does not hatch. Therefore, in cases where both eggs hatch, the second offspring could represent an extra energetic burden on the parent birds to feed it, particularly in years of low food supply (8) (9). The remaining chick fledges after around 115 days (6), but does not reach sexual maturity and begin breeding until three to four years old (3).