Culpepper (Darwin) Island, Galapagos Archipelago.
Until recently considered conspecific with S. dactylatra, but breeds sympatrically and assortatively with it, differing in its orange (not yellow) bill and greater sexual dimorphism; compared with sympatric form personata, has shallower bill, shorter tarsus and longer wing; legs and feet olive-khaki to purple vs bright yellowish in dactylatra, but dark bluish-grey to olive-grey in personata; also differs in foraging preference, concentrating near shore, not out to sea; and in typical use of steep slopes, and not flat areas, for nesting. Monotypic.
Breeds on islands in CE Pacific from NW Mexico S, including Revillagigedo Is, Clipperton I, Cocos I (S of Costa Rica) and Malpelo I (off W Colombia), to Galapagos Is, La Plata I (Ecuador) and, more recently, Lobos de Afuera (NW Peru).
Food and feeding
Status and conservation
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