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Genetic and temporal patterns of multiple parasitism by brown-headed cowbirds (Molothrus ater) on song sparrows (Melospiza melodia)

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Identifying the factors used by an avian brood parasite to select host nests is important in understanding the determinates of individual reproductive success, yet such factors are poorly known for most parasitic species. Insights into these factors may come from understanding the conditions under which female parasites lay more than one egg per host nest (multiple parasitism). Using genetic techniques we examined patterns of multiple parasitism on a preferred host, the song sparrow (Melospiza melodia), to determine some basic patterns of multiple parasitism. Multiple parasitism involved equal frequencies of the same female parasitizing the same nest again and two or more females parasitizing the same nest. The frequency of multiple parasitism increased as the season progressed. We also documented a high frequency of parasitism that was not synchronized with host laying. These laying patterns may be the result of cowbirds "making the best of a bad situation" or of suboptimal host choice by inexperienced, nonselective females.

L'identification des facteurs qu'utilisent les parasites des nids d'oiseaux pour choisir les nids de leurs hôtes est essentielle à la compréhension des variables déterminantes du succès de leur reproduction individuelle, et pourtant ces facteurs sont mal connus pour la plupart des parasites. La compréhension des conditions dans lesquelles les parasites femelles pondent plus d'un oeuf par nid (parasitisme multiple) peut jeter de la lumière sur la question. Nous avons tenté de déterminer les patterns de base du parasitisme multiple au moyen de techniques génétiques chez un hôte de prédilection, le bruant chanteur (Melospiza melodia). Le parasitisme multiple est le fait tant des femelles qui pondent deux fois ou plus dans le même nid, que de plusieurs femelles qui pondent dans le même nid. La fréquence du parasitisme multiple augmente à mesure que la saison progresse. Nous avons également observé plusieurs cas de parasitisme multiple non synchronisé avec la ponte de l'hôte. Ces patterns sont probablement des pontes de vachers qui tirent le meilleur parti possible d'une situation boiteuse au départ ou la conséquence d'un choix d'hôte sub-optimal par une femelle non sélective et inexpérimentée.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2003-02-01

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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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