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  • Cowbirds change their eggs’ sex ratio based on breeding time

    A female, left, and male cowbird perch on a wire fence. They appear to be looking at one another. Both birds are adults.

    A new study finds that cowbirds adjust the sex of their offspring throughout the nesting season. A female, left, and male cowbird perch on a wire fence. Both birds are adults.

    Photo by Michael Jeffords and Sue Post

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  • Editor’s notes:

    To reach Mark Hauber, email mhauber@illinois.edu.
    To reach Wendy Schelsky, email schelsky@illinois.edu.
    The paper “A seasonal shift in offspring sex ratio of the brood parasitic brown-headed cowbird (Molothrus ater)” is available online and from the U. of I. News Bureau.
    DOI:  https://doi.org/10.1111/jav.02560

    Michael Jeffords and Sue Post are wildlife photographers and research affiliates of the Illinois Natural History Survey at the Prairie Research Institute of the U. of I. Their photographs are available here.