Brown-headed cowbirds don’t exactly make the best parents. They drop their eggs in other birds’ nests and leave it to those birds to do the hatching and raising. As BirdNote®’s Michael Stein tells us, the yellow warbler is a frequent recipient of the cowbird’s eggs. In the photo--The Brown-headed Cowbird lays her eggs in other birds’ nests. (Photo: Tom Grey ©)
GELLERMAN: It’s Living on Earth, I’m Bruce Gellerman.
GELLERMAN: Birds do it - and most take the same approach to parenthood - they lay their eggs in nests then incubate them until the nestlings hatch. But some birds do it differently, as BirdNote®’s Michael Stein tells it.
[BROWN-HEADED COWBIRD SONG AND CALL]
STEIN: It seems that nature doesn’t always play fair. One notorious avian example: the behavior of Brown-headed Cowbirds.
STEIN: Cowbirds, which are found throughout much of North America, lay their eggs in other birds’ nests and these birds raise the cowbird chicks, often at the expense of their own young.
STEIN: The beautiful Yellow Warbler is a frequent target of the cowbird’s unwelcome eggs. But it has developed a way to reject the role of foster parent. When a cowbird lays its egg in a Yellow Warbler’s nest, a tiny compact cup woven of plant fibers, the warbler weaves another layer of grasses over the top of the cowbird egg, preventing its incubation. Sometimes a cowbird returns and lays another egg in the same nest and now the Yellow Warbler covers over the second egg. Amazingly, one Yellow Warbler nest in Ontario grew six layers deep. Cowbirds developed their habit of palming off their eggs on other birds because they followed migrating herds of buffalo - cowbirds couldn’t stay in one place long enough to raise their own young. Today, it’s still a problem that even the hardest working Yellow Warbler is sometimes challenged to overcome.
GELLERMAN: That’s Michael Stein of BirdNote®. You’ll find a flock of photos on our website loe.org.
Sounds of the birds provided by The Macaulay Library of Natural Sounds at the Cornell Lab of Ornithology, Ithaca, New York. Song and call together recorded by D.S. Herr; song of Yellow Warbler recorded by M.J. Anderson.
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