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Brown-headed Cowbird: Brood Parasite

One has to admire a creature who has managed to eliminate the laboriousness of raising its offspring.  Brown-headed Cowbirds, renowned brood parasites, have done just that.  These birds do not build nests; females lay up to 40 eggs a summer in the nests of more than 220 species of birds which raise their young for them.  Cowbird eggs are generally larger than the host bird’s and hatch in fewer days, thereby putting Cowbird chicks at a distinct advantage over the host’s chicks when it comes to parental attention.

In this photo a Brown-headed Cowbird has deposited three eggs in the nest of an Eastern Phoebe (which has constructed its nest inside an abandoned American Robin nest). Unlike some songbirds, Phoebes do not recognize and remove the Cowbird’s eggs. Neither do they build a new nest on top of the old one, as some smaller songbirds (i.e. Yellow Warblers) are known to do.

Cowbird chicks develop faster than the chicks of the host bird, thereby often getting the first crack at the food parents bring to the nestlings.  Not only are the host species’ chicks often at a disadvantage when it comes to parental care, but they are at the mercy of the Cowbird chicks which often remove both the eggs and chicks of the host. (Thanks to friends in Thetford, VT for the use of their photograph of this parasitized Eastern Phoebe nest. The three larger, speckled eggs are Brown-headed Cowbird eggs; the four smaller white eggs are Eastern Phoebe eggs.)

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12 responses

  1. Are there both phoebe and robin eggs in that nest? It may be the camera angle, but the unspeckled eggs look two different sizes to me.

    May 28, 2021 at 9:15 am

  2. Alice

    I’m wondering if there are any advantages to any kind of parasite? Seems sad that the Brown-headed Cowbird has evolved this way, instead of taking care of its own young. Saw a few here, earlier this Spring. Phoebe eggs are pretty!

    May 28, 2021 at 10:30 am

  3. Alice

    I’m wondering if there are any advantages to any kind of parasite. It’s sad that the Brown-headed Cowbird has evolved this way, instead of taking care of it’s own young. Seen a few earlier this Spring, but they seemed to have flown away. Phoebe eggs are pretty.

    May 28, 2021 at 10:33 am

  4. Alice

    Oops…didn’t see my comment…so wrote again.

    May 28, 2021 at 10:34 am

  5. Bill on the Hill

    This is nature at it’s best? It certainty works out as designed for the cowbird…It brings to mind certain elements of the human population, i.e. having children with reckless abandon without a thought towards raising or feeding them…
    I believe the (4) eggs are of the same specie of bird & it is the angle of light making 2 of them appear yellowish. If memory serves me correct, Robin eggs are bluish in reference to the Pratt comment…
    Bill… :~)

    May 28, 2021 at 10:37 am

  6. Maggy

    And since cowbirds have nothing better to do with their time, they perch on the rear view mirrors of my car, seeming to admire themselves in the windows and mirrors.

    May 28, 2021 at 10:46 am

    • Really? (re. your comment, Maggy.) That’s amazing.
      Hearing all these details about cowbirds reminds me of the Mayzie character in “Horton Hatches an Egg.”

      May 28, 2021 at 12:04 pm

  7. I wonder, Mary, whether if you happened on that nest you would be tempted to remove the cowbird eggs. I think I would.

    May 28, 2021 at 1:28 pm

    • Alice

      Kathie: I sent my daughter this post & she wrote back, with photos from Audubon.org about if it’s OK to remove Cow bird eggs from host nests.

      May 28, 2021 at 1:36 pm

      • Thanks Alice. Very interesting – for those interested, the website is https://www.audubon.org/news/is-it-okay-remove-cowbird-eggs-host-nests

        May 28, 2021 at 2:11 pm

      • Thank you, Alice. I got interested in cowbirds a few years ago when I watched a pair slowly wandering through the grass behind our house, looking around–I assume searching for song sparrow nests. They are interesting critters, and the Audubon post makes it very clear that we should let them be!

        May 31, 2021 at 8:40 am

  8. Must be in the same family!! They sound like a Red Winged Blackbird! 🙂 ❤ We have had these! They are Lovely!

    https://www.allaboutbirds.org/guide/Brown-headed_Cowbird/media-browser/409919

    May 28, 2021 at 5:10 pm

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