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The Breeding Biology of the Pied Water-Tyrant and Its Interactions with the Shiny Cowbird in Venezuela (La Biología Reproductiva de Fluvicola pica y su Interacción con Molothrus bonariensis en Venezuela)

Alexander Cruz and Robert W. Andrews
Journal of Field Ornithology
Vol. 68, No. 1 (Winter, 1997), pp. 91-97
Published by: Wiley on behalf of Association of Field Ornithologists
Stable URL: http://www.jstor.org/stable/4514197
Page Count: 7
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Breeding Biology of the Pied Water-Tyrant and Its Interactions with the Shiny Cowbird in Venezuela (La Biología Reproductiva de Fluvicola pica y su Interacción con Molothrus bonariensis en Venezuela)
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Abstract

We studied the breeding biology of the Pied Water-Tyrant (Fluvicola pica) in a seasonally inundated savanna in the llanos of western Venezuela. A total of 123 nests was located in the wet season (June-October). The water-tyrant nested mainly in trees and shrubs near water in the early part of the wet season (86%), but nested primarily in emergent marsh vegetation during the latter part (84%). The species was heavily parasitized (53% of nests) by the Shiny Cowbird (Molothrus bonariensis). The rate of parasitism was nearly equal in both tree/shrub nests and marsh nests, and declined only late in the season. Parasitized nests were more frequently abandoned (60%) than nonparasitized nests (30%). The number of host eggs in nests was nearly equal in non-parasitized (2.42) and parasitized nests (2.51). The number of cowbird eggs (1.23) was less than the number of host eggs in parasitized nests. Of 37 non-parasitized clutches of the Pied Water-Tyrant, 18 (49%) produced nestlings and 7 (19%) produced fledglings, and of 47 parasitized clutches, 2 (4%) produced nestlings and fledglings. Given the high level of parasitism on the Pied Water-Tyrant, it should be considered a major Shiny Cowbird host in the llanos of Venezuela. The Pied Water-Tyrant, however, does not appear to be an optimal host as only 3 of 47 parasitized nests in which the outcome was known successfully fledged cowbird young. /// Estudiamos la biología reproductiva de Fluvicola pica en una sabana estacionalmente inundada en los llanos del oeste de Venezuela. En la temporada húmeda (junio-octubre) se localizaron un total de 123 nidos. En la parte temprana de la temporada húmeda la especie anidó principalmente en árboles y arbustos cerca del agua (86%), pero anidó principalmente en vegetación pantanosa emergente durante el final de temporada (84%). La especie fué intensamente parasitada (53% de los nidos) por Molothrus bonariensis. La razón de parasitismo fué prácticamente igual tanto en árboles/arbustos como en nidos de pantanos, y declinó solo al final de la temporada. Los nidos parasitados fueron abandonados más frecuentemente (60%) que los no parasitados (30%). En número de huevos de la especie hosperdera por nido fué casi igual en los nidos no-parasitados (2.42) y en los parasitados (2.51). El número de huevos de Molothrus (1.23) fué menor que el número de huevos de Fluvicola en nidos parasitados. De 37 camadas no parasitadas de Fluvicola pica, 18 (49%) produjeron pichones y 7 (19%) produjeron volantones, mientras que de 47 camadas parasitadas, 2 (4%) produjeron pichones y volantones. Debe considerarse Fluvicola pica como uno de los hosperderos principales de Molthrus bonariensis en los llanos de Venezuela dado el alto nivel del parasitismo detectado. Sin embargo, Fluvicola pica no parece ser un hospedero óptimo ya que solo 3 de 47 nidos parasitados en los cuales se conoce el éxito sacaron volantones de Molothrus.

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