eWestern Birds

The Quarterly Journal of Western Field Ornithologists

Vol. 52, No. 1
February 2021
Western Field Ornithologists

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Evidence of Brood Parasitism and Quantification of Rangewide Overlap between the Olive Warbler and Brown-headed Cowbird
Jessie L. Williamson and Matthew J. Baumann

ABSTRACT: Brood parasitism is a fascinating natural history phenomenon that provides a window into the coevolution of antagonistic interactions. Many ecological and evolutionary aspects of brood parasitism remain unknown, and new hosts of brood parasites are still being discovered. We document the second instance of brood parasitism of the Olive Warbler (Peucedramus taeniatus) by the Brown-headed Cowbird (Molothrus ater). Apparent lack of habitat and elevation overlap across the ranges of these two species prompted us to examine how frequently they come into contact. We analyzed >3 million Olive Warbler and Brown-headed Cowbird occurrence records from two open-source repositories, eBird and GBIF, to examine both synchronous and asynchronous locality overlap during the breeding season. We found that the two species were documented together simultaneously in only 3.1% of analyzed instances, but that they co-occurred in similar habitat types and/or at similar elevations at 11.8% of localities analyzed across the Olive Warbler’s range. Additional research on aspects of ecology and evolution, such as host selection, the cowbird’s diurnal patterns of movement, and the dynamics of intracellular pathogens infecting brood parasites and their hosts, may shed light more broadly on the ecological interactions and mechanisms underlying brood parasitism.

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