The yellow-shouldered blackbird (Agelaius xanthomus), known in Puerto Rican Spanish as mariquita de Puerto Rico or capitán, is a species of blackbird endemic to Puerto Rico. It has black plumage with a prominent yellow patch on the wing. Adult males and females are of similar appearance. The species is predominantly insectivorous. Taxonomy The nominate form of the yellow-shouldered blackbird (A. x. xanthomus) was first described from Puerto Rico and Vieques in 1862 by Philip Sclater as Icterus xanthomus. The recognized subspecies A. x. monensis, or Mona yellow-shouldered blackbird, was described by Barnes in 1945 from the islands of Mona and Monito. The species is closely related to, and possibly derived from, the red-winged blackbird (Agelaius phoeniceus). The tawny-shouldered blackbird (Agelaius humeralis), a species from Cuba and Hispaniola, is morphologically intermediate between A. xanthomus and A. phoeniceus. Until recently, some authors considered A. xanthomus as a subspecies of A. humeralis. The 1983 American Ornithologists' Union edition considered A. xanthomus, together with A. humeralis, a superspecies. The main physical difference between A. xanthomus and A. humeralis resides in their bills, with that of A. humeralis being broader toward the base. Description The yellow-shouldered blackbird, as its name implies, is a glossy black bird with a small yellow humeral patch around its "shoulders" outlined by a white margin. Immature individuals possess a duller coloration and a brown abdomen. Although plumage coloration is indistinguishable between the sexes, sexual dimorphism is present in this species with males being larger than females. Plumage abnormality is rare in this species. Adult individuals measure from ; on average, males weigh and females weigh . Sexual categorization may also be made by measurement of the wings, with males' being 1.1 times larger and having a mean length of , while females' wings have an average length of . Conservation and habitat The species was once commonly found in the coastal forests of the archipelago of Puerto Rico, but during the early 20th century, these forests were cut down to allow for the development of sugarcane plantations. After the decline of the sugar industry after the 1930s the coastal areas were developed for housing. As a result, the species is now limited to three areas: the islands of Mona and Monito, where a subspecies developed (A. g. xmonensis); the Roosevelt Roads Naval Station area in eastern Puerto Rico; and the southern Puerto Rican dry forests and mangroves. Although all three