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Cooperative Warbling Vireo Nestlings

6-27-17 fecal sac 117Shortly after being fed, most songbird nestlings produce what is called a fecal sac – a mucous membrane (usually white with a dark end) that contains their excrement. This sac enables easy removal of the chicks’ waste by the parents. In an effort to keep its young healthy and to reduce the chances of predators finding the nest, the parent takes the fecal sac in its beak, flies away and discards it some distance from the nest.

Some nestlings, including those of Warbling Vireos, are extremely cooperative when it comes to assisting their parents in keeping the nest clean.  Just prior to producing a fecal sac they position themselves with their rear ends up in the air (see photo), where their parents can easily procure the fecal sacs when they appear.

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11 responses

  1. Pauline Bogaert

    Amazing housekeeping!

    June 27, 2017 at 6:59 am

  2. Alice Pratt

    More interesting facts. I’m relieved (!!!) that human babies wear diapers 😝

    June 27, 2017 at 7:01 am

  3. Thank you for explaining why there were never droppings beneath the nests of the phoebes and swallows around our sun porch. I wonder where they put ’em…

    June 27, 2017 at 7:51 am

  4. judilindsey


    Simply amazing! What a terrific way to keep the house clean!

    Thanks, Judi


    June 27, 2017 at 7:54 am

  5. John Cannon

    And we think humans are so sophisticated and smart. Birds have been on the planet for about 65 million years (human beings about 200,000 years). Maybe we should all pay a little closer attention to birds and learn a thing or two. Thanks Mary.

    June 27, 2017 at 2:59 pm

  6. Great shots. I’ve been watching the house wrens on the shed doing the housekeeping, too.
    BTW, I was wondering, if a nestling dies, do the parents remove it? I expect they would, but do you know?

    June 27, 2017 at 8:10 pm

    • I know some species do remove their dead nestlings, but not sure which ones, or how many, Eliza.

      June 29, 2017 at 3:16 pm

  7. Oh, for goodness sake! How can it be that I never knew about this?? I am amazed and charmed!

    June 27, 2017 at 9:53 pm

  8. Susan Fraser

    Really nice photo! A few years ago, I first learned of this practice when watching a nest of Robins. This year, I watched Phoebes doing the same thing. As they got older the young would be fed then immediately turn around and up-end. I wonder if this is common with most birds nesting in trees or boxes.

    July 6, 2017 at 6:18 pm

    • A friend observed bluebird nestlings doing this, too. Maybe they all do it!

      July 6, 2017 at 7:51 pm

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