Brown-headed Cowbird parasitism of the Black-throated Sparrow in central Arizona

Journal of Field Ornithology
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From 1994-1996 we investigated effects of Brown-headed Cowbird (Molothrus ater) parasitism on Black-throated Sparrow (Amphispiza bilineata) nesting success in the Verde Valley of central Arizona. Of 56 Black-throated Sparrow nests, 52% were parasitized. Black-throated Sparrows appear to respond to natural parasitism by accepting the cowbird egg, deserting the nest, or burying the cowbird egg. Removal and damage of host eggs by female cowbirds effectively reduced clutch size from an average of 3.4 to 1.9 eggs. Because of this reduced clutch size, Black-throated Sparrow reproductive success was significantly lower in parasitized nests (0.2 young fledged/ nest) as compared to nonparasitized nests (1.6 young fledged/nest). When comparing cowbird parasitism between two habitat types, we found significantly higher parasitism frequencies in crucifixion-thorn (Canotia holacantha) versus creosote-bush (Larrea divaricata) habitat. We argue that this difference in parasitism is due to the greater number of tall perches (e.g., shrubs >4 m) available in crucifixion-thorn habitat, providing vantage points for female cowbirds to better find Black-throated Sparrow nests.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Brown-headed Cowbird parasitism of the Black-throated Sparrow in central Arizona
Series title Journal of Field Ornithology
Volume 75
Issue 3
Year Published 2004
Language English
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Journal of Field Ornithology
First page 303
Last page 311