JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. University of California Press and AmericanOrnithologists' Union are collaborating with JSTOR to digitize, preserve and extend access to Ornithological Monographs.Abstract.-Historically, the Shiny Cowbird (Molothrus bonariensis; hereafter "cowbird") was confined to South America, Trinidad, and Tobago. Within the past century, cowbirds have expanded their range into the West Indies, bringing them into contact with avian communities that have never experienced brood parasitism. Because of their small populations, high degree of isolation, and lack of experience with cowbirds, West Indian birds are at greater risk of harm from cowbird contact than mainland birds. Cowbird parasitism was the single most important factor in the reduced reproductive output of the endangered Yellow-shouldered Blackbird (Agelaius xanthomus; hereafter "blackbird"), a Puerto Rican endemic. Roost counts estimated that the blackbird population declined in southwestern Puerto Rico from 1,663 individuals (1974)(1975) to 266 (1981-1982). Cowbird trapping in upland areas near blackbird nesting areas in mangroves and cowbird feeding areas has proved successful in managing cowbirds and increasing blackbird populations. Removal of cowbird eggs and nestlings from artificial nesting structures has resulted in fewer parasitized blackbird nests. As a result of those measures, cowbird parasitism of blackbirds has fallen from 95% (1973-1983) to <3% (2000-2003) and, judging from roost counts in 2004, the blackbird population has increased to 800 individuals in southwestern Puerto Rico. Cowbird management programs have excellent potential to reduce the adverse effects of cowbird parasitism; however, trapping within nesting areas is not recommended, because it may increase *he probability of capturing and stressing breeding blackbirds. Resumen.-Historicamente, Molothrus bonariensis estaba confinado a Sudamerica, Trinidad, y Tobago. A lo largo del siglo pasado, Molothrus bonariensis ha expandido su area a las IndiasOrientales, lo que los ha puesto en contacto con comunidades de aves que nunca antes habian experimentado el parasitismo de cria. Debido a su pequeno tamano poblacional, alto grado de aislamiento, y falta de experiencia previa con Molothrus, las aves de las Indias Orientales estan en un mayor riesgo de dano causado por los tordos que las especies continentales. El parasitismo por el Molothrus bonariensis fue el unico y mas importante factor responsable de la reduccion del exito reproductivo de Agelaius xanthomus, una especie en peligro endemica de Puerto Rico. Mediante conteos en dormideros se estimo que la poblacion Agelaius xanthomus disminuyo en el sudeste de Puerto Rico de 1,663 individuos (1974-1975) a 266 (19...
Avian immunology developed originally by investigating domesticated poultry species (Galliformes), but in recent decades eco-immunological studies of wild bird species have revealed that avian immune systems are more diverse than initially assumed. This study compares six immunological elements in eggs of six species within the same family, the New World blackbirds (Icteridae),whose members differ most notably in two life history parameters, brood parasitism and body size. We measured the maternal immune investment of passive immune components in both yolk and albumen: lysozyme, ovotransferrin, and immunoglobulins (Igs), and LPS-specific Igs. We predicted that brood parasites would have higher levels of immune activity for both innate and adaptive immunity compared with non-brood parasites, and that increased body size could increase microbial exposure of larger animals, resulting in an increase in some adaptive immune responses, such as LPS-specific Igs. We found that brood parasites had significantly higher levels of Igs and lysozyme levels in albumen, but significantly lower levels of Igs in yolk compared with non-brood parasites. Igs in yolk scaled according to body size, with the smallest organisms (the brood parasites) having the lowest levels, and the largest organism (common grackle) having the highest. Our results confirm the findings of other studies of comparative immunity among species in a single taxon that (1) similarities in immune investment cannot be assumed among closely related species and (2) single measures of immune defense cannot be assumed to be indicators of a species’ overall immune strategy, as life history traits can differentially affect immune responses.
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