|Adult on Española Island, Galapagos Islands|
The Nazca booby (Sula granti) is a colonial seabird in the family Sulidae, native to the eastern Pacific.
Walter Rothschild organised and sent an expedition to the Galapagos Islands in 1897 to collect and review the animal life there. He wrote of a distinctive booby there, which he and William Robert Ogilvie-Grant diagnosed as the Peruvian booby (Sula variegata), then only known from juvenile plumage. Later, in 1802, Rothschild named it a new species, Sula granti. Rothschild later reclassified as a subspecies of the masked booby.
The genus Sula was previously placed in the order Pelecaniformes, but recently was collected in the family Sulidae and order Suliformes, together with 8 other genera. The Nazca booby was considered conspecific with the masked booby but was reassigned to a separate species based on mitochondrial DNA analyses. It is likely to have diverged 400,000-500,000 years ago.
The species has a yellow iris, orange and pinkish beak, black facial skin in the form of a mask, and grey feet. Adults present white plumage with black tips of the wings and tail. The female is bigger and heavier than the male, has a slightly differently colored beak, and squawks while the male whistles. Chicks are snow white and fluffy, plumage changing to grey along with beak and feet upon fledging.
Distribution and habitat
The Nazca booby preys on small fish caught by diving at high speed from flight into the ocean. The main food species is South American pilchard, but also take flying fish, anchovies and squid, specially during the El Niño events, when sardine numbers are low. Because of their sexual dimorphism, females tend to feed on bigger prey and dive deeper.
Like many seabirds, the species has a long lifespan combined with low annual reproduction and long periods of development in the young. Clutch size is one or two eggs, due to the low hatching success, however when 2 eggs are laid and they both hatch, it is common for only one of the chicks to survive.
While many species of birds regulate egg temperature via an incubation patch, a layer of bare skin that allows birds to transmit heat into their eggs, the Suliformes instead use the skin on their webbed feet in addition to heat transferred from the breast. The feet are heavily vascularized, especially during the nesting period. Both the male and the female show parental care. Usually the chick that hatches first is bigger and becomes aggressive towards its sibling, excluding it from feeding and eventually starving it.
The energy investment on the parent’s part is very high, so their metabolic rates change during the nesting season. This causes both parents to lose similar amounts of body weight and suffer a decline in their immune system activity. This adjustment does not take place when the parents decide not to nest, a decision that is mostly driven by food availability, which in turn depends on ocean current and climate patterns such as those driven by the El Niño oscillation.
Siblicide has been well studied in this species; the first chick is born around five days before the second and is larger and stronger by the time the second is born. It drags its younger sibling out of the nest. Field experiments in the Galapagos demonstrated that the boobies can manage to feed two chicks without too much difficulty. This raises questions as to the origin of the phenomenon. 
The Nazca booby is classified as Least Concern by the IUCN. Although populations are thought to decrease to some extent, this decline is not strong enough to require classification in a threat category. Some of the factors that influence the decrease of populations are overfishing and marine pollution.
- BirdLife International (2012). "Sula granti". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature.
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- Rothschild, Walter (1902). "An overlooked species of gannet". Bulletin of the British Ornithologists' Club. 13: 7.
- Rothschild, Walter (1915). "Notes on the genus Sula". Bulletin of the British Ornithologists' Club. 35: 41-45.
- Pitman, Robert L.; Jehl, Joseph R.; Joseph L. Jehl (1998-01-01). "Geographic Variation and Reassessment of Species Limits in the "Masked" Boobies of the Eastern Pacific Ocean". The Wilson Bulletin. 110 (2): 155–70. JSTOR 4163925.
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- Ridgely, R. S.; Greenfield, P.J. (2006). Aves del Ecuador. Guía de Campo. Fundación de Conservación Jocotoco. p. 92.
- "Nazca Booby (Sula granti) - BirdLife species factsheet". www.birdlife.org. Retrieved 2016-10-01.
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- Crawford, R. J. M.; Goya, E.; Roux, J.-P.; Zavalaga, C. B. (2006-11-01). "Comparison of assemblages and some life-history traits of seabirds in the Humboldt and Benguela systems". African Journal of Marine Science. 28 (3–4): 553–560. doi:10.2989/18142320609504205. ISSN 1814-232X.
- García-R, Silvana; López-Victoria, Mateo (2008-12-15). "Sexual differences in body size and diet in the Nazca Booby (Sula granti)" (7). ISSN 1794-0915.
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- Maness, Terri J.; Anderson, David J. (2007-01-01). "Serial Monogamy and Sex Ratio Bias in Nazca Boobies". Proceedings: Biological Sciences. 274 (1621): 2047–2054. doi:10.1098/rspb.2007.0578. JSTOR 25249287. PMC 2275186. PMID 17567557.
- Anderson, David J. (1990). "Evaluation of Obligate Suicide in Boobies. 2: Food Limitation and Parent-Offspring Conflict". Evolution. 44 (8): 2069–82. JSTOR 2409616.
- Anderson, David J. 1990. "Evolution of Obligate Siblicide in Boobies 1. A Test of the Insurance-Egg Hypothesis." The American Naturalist 135, vol. 3: 334-350
- Takasuka, Akinori; Oozeki, Yoshioki; Aoki, Ichiro (2007-05-01). "Optimal growth temperature hypothesis: Why do anchovy flourish and sardine collapse or vice versa under the same ocean regime?". Canadian Journal of Fisheries and Aquatic Sciences. 64 (5): 768–776. doi:10.1139/f07-052. ISSN 0706-652X.
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