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Host community-wide patterns of post-fledging behavior and survival of obligate brood parasitic brown-headed cowbirds


The antagonistic arms races between obligate brood parasites and their hosts provide critical insights into coevolutionary processes and constraints on the evolution of life history strategies. In avian brood parasites—a model system for examining host–parasite dynamics—research has primarily focused on the egg and nestling stage, while far less is known about the behavior and ecology of fledgling and juvenile brood parasites. To provide greater insights into the post-fledging period of generalist brood parasites, we used handheld and automated telemetry systems to examine the behavior and survival of fledgling brown-headed cowbirds (Molothrus ater). Our host community-wide analysis (data on cowbirds fledged from different host species were pooled) shows that fledgling cowbirds’ follow patterns of movement and survival found across the post-fledging literature on parental passerine species. Cowbird fledgling survival was lowest during the first 3 days post-fledging, whereas daily rates of survival neared 100% after about 16 days post-fledging. Cowbird daytime post-fledging activity rates, perch heights, and distance from the natal area all increased with fledging age and young generally gained independence from host parents at 3–4 weeks post-fledging, with approximately the same latency as has been observed in studies on fledglings of cowbird host species. Our research demonstrates how automated telemetry systems can overcome past methodological limitations in post-fledging research and provides an important foundation for future studies examining adaptations that cowbirds and other brood parasites use to exploit hosts during the post-fledging period.

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Upon acceptance, data for this manuscript will be uploaded to the Illinois Databank,


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This work would not be possible without the dedicated efforts of Alex DiGiovanni, Nicole Suckow, Kara Winter, Abby Riggs, Nisarg Shah, Mia Larrieu, Michael Miller, Evalynn Trumbo, and Ryan Leeson. We are grateful to Kennekuk Cove County Park for access to our study site and help in the field and to the Middlefork Audubon Society for access to nest boxes.


This research was funded through Federal Aid in Wildlife Restoration from the Illinois Department of Natural Resources and U.S. Fish and Wildlife Service (project W-154-R; to MPW), and research grants from the Illinois Ornithological Society, Association of Field Ornithologists, Wilson Ornithological Society, American Ornithological Society, The North American Bluebird Society, and Inland Bird Banding Association (to TMJ). This work was also supported by the USDA National Institute of Food and Agriculture, Hatch project ILLU-875-963 (to MPW). Additional support was provided by the Center for Advanced Study at the University of Illinois and the Wissenschaftskolleg zu Berlin, Germany (to MEH).

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Authors and Affiliations



TMJ and MPW conceived the study, which they designed with TJB and MEH. TMJ collected the data, led the analyses, and wrote the manuscript; all other authors helped write the manuscript and provided editorial advice.

Corresponding author

Correspondence to Todd M. Jones.

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Conflict of interest

The authors have no conflicts of interest or competing interests.

Ethics approval

All applicable institutional and/or national guidelines for the care and use of animals were followed; animal care and use were approved by the Institutional Animal Care and Use Committee at the University of Illinois at Urbana-Champaign, protocol no. 18221. All capture and banding practices were covered under a US Fish and Wildlife Service Master Bander Permit #23875 (to TMJ).

Additional information

Communicated by Kathryn E. Sieving.

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Jones, T.M., Benson, T.J., Hauber, M.E. et al. Host community-wide patterns of post-fledging behavior and survival of obligate brood parasitic brown-headed cowbirds. Oecologia 198, 981–993 (2022).

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  • Post-fledging
  • Cowbird
  • Brood parasite
  • Songbird
  • Fledgling
  • Activity
  • Survival