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Gregory R. Mann, Ph.D. {ret.}

Peruvian Booby

“Sula variegata”

The Peruvian Booby is a bird of the Humboldt current off western South America. It is the second most abundant seabird species that inhabits the Peruvian Coast and the second most important guano-producing seabird. The word “booby” comes from the Spanish “bobo” meaning “stupid fellow” and was probably inspired by the bird’s clumsiness on land. They are extremely vulnerable to human visitors because they do not appear to fear us. During the mid-twentieth century, the Peruvian Booby population reached 3 million birds. Like the Blue-footed Booby, the Peruvian Booby has brown upper-parts, a gray bill and white head & underparts. Peruvian Boobies however, have gray rather than blue legs, a whiter head, more white mottling on the upper-wings and no white patch at the center of the lower back. This species breeds from northern Peru to central Chile on small coastal islands on cliff ledges or bare ground. While generally rather sedentary, El Niño events may trigger massive dispersal & vagrancy north to Colombia and south to southern Chile. During these events, the up-welling patterns of coastal Peru and Chile are altered and the food sources that the Peruvian Booby and other seabirds depend on are effectively cut off. Typically however, this species feeds in groups, often with other seabirds by plunge-diving in pursuit of schooling fish such as anchovies.

Peruvian Boobies breed throughout the year. Main breeding season occurs during the austral spring-summer period (September to March) and most pairs may attempt to breed for a second time during the year depending on food availability. They performed short foraging trips, varying between a few minutes and several hours. Average foraging range was 3.5 kilometers and diving took place between 2 to10 kilometers off the coast. Birds dove to depth of up to 10 meters with an average depth of 1.5 meters. Peruvian Boobies clutch size varies from 1 to 4 eggs, but clutches of 2 or 3 eggs, pale blue in color are usually found. Eggs are incubated during approximately 4 to 5 weeks, both adults share the nest attendance. The rearing period lasts about 3 months. Breeding success depends on food availability and is related to colony location, colony size & timing of breeding which is September through February in Peru, much later in Chile. Breeds in immense colonies where nests consist of loose pile of seaweed & debris, stuck together with excreta. Lays 3 eggs on average, which are incubated for 42 days. Chicks fledge at 78–105 days and are cared for a further 62 days on average. First breeding occurs at 2 to 3 years of age. Peruvian Boobies normally live along the western coastline of South America from Chile to southern Ecuador some 600 miles966 kilometersto the east of the Galápagos Islands where they feed on anchovies that thrive in the cold, productive water of the Humboldt Current. In a typical year, the birds don’t stray much farther than 40 miles (64 kilometers) from their homes. Peruvian Boobies are known for abandoning their normal feeding grounds when a strong El Niño hits, sometimes traveling as far as Panama (850 miles, or 1,368 kilometers) in search of food. During El Niño conditions, the likelihood of citing vagrant is much higher than during normal, non-El Niño conditions.

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