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Site selection and repeatability in Brown-Headed Cowbird (Molothrus ater) parasitism of Eastern Phoebe (Sayornis phoebe) nests

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Abstract:

The reproductive success of obligate brood parasitic birds depends on their ability to seek out heterospecific nests. Some nests are more suitable for parasitism than others and, for example, parasitic females may benefit from laying eggs preferentially and repeatedly at safer sites. Observations on patterns of Brown-headed Cowbird (Molothrus ater) parasitism on Eastern Phoebes (Sayornis phoebe) across 2 years suggested that parasitism occurred at above chance levels during the first rather than the second nesting attempts and at nests located under eaves rather than bridges. Previously parasitized nests were more likely to be parasitized again in the subsequent breeding season. Sites under eaves and bridges did not differ in whether Brown-headed Cowbirds could be detected in the proximity of the nest. However, nests from first nesting attempts and nests under eaves were less likely to be lost as a result of structural failure of the Eastern Phoebe's mud nest. These data suggest that site discrimination by Brown-headed Cowbirds leads to adaptive patterns of parasitism among available Eastern Phoebe nests.

Le succès de la reproduction des nicheurs parasites obligés dépend de leur aptitude à trouver des nids d'oiseaux hétérospécifiques. Certains nids se prêtent mieux au parasitisme et, par exemple, les femelles parasites ont intérêt à pondre de préférence et à répétition aux sites les plus sûrs. L'observation de la ponte pendant 2 ans chez des Vachers à tête brune (Molothrus ater) parasites de nids de Moucherolles phébi (Sayornis phoebe) a indiqué que le parasitisme atteignait des niveaux supérieurs au niveau aléatoire au cours de la première tentative de nidification plutôt qu'au cours de la seconde et dans les nids sous les avant-toit plutôt que dans les nids sous les ponts. Les nids parasités antérieurement étaient plus susceptibles d'être parasités de nouveau au cours de la saison de reproduction suivante. La probabilité de détection des Vachers à tête brune à proximité des nids ne différait pas entre les sites sous les avant-toit et les sites sous les ponts. Cependant, les nids de boue des Moucherolles phébi construits lors d'une première tentative et les nids construits sous les avant-toit avaient moins de chance d'être perdus à la suite d'une rupture structurale. Ces données indiquent que les Vachers à tête brune sont capables de discrimination des sites, ce qui entraîne l'établissement de patterns évolutifs de parasitisme dans les nids de Moucherolles phébi disponibles.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: August 1, 2001

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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