What would you do if someone left a baby on your doorstep? What if you thought the child was yours? Some birds are quite clever at making others think just that. By giving their young to unwitting "foster parents", the birds have permanent baby-sitters, and they don't have to do any of the hard work it takes to raise young!
Brown-headed cowbirds, one type of "nest parasite", live in the Chihuahuan Desert. The female searches for a nesting bird, perhaps a red-winged blackbird, and when the parents are away, she swoops down and lays an egg of her own in the nest. She usually destroys one of the blackbird eggs, keeping the number of eggs the same so no one is likely to notice the change.
The young cowbird usually hatches before its nestmates, so it gets a
head start over the blackbird young! Baby cowbirds are ravenous eaters, and they beg
aggressively, so the blackbird parents must work, non-stop, to keep this voracious
child fed! Inevitably, the cowbird gets more food than the other young, sometimes
dooming them. This gives a whole new meaning to the phrase "switched at
birth"!
Listen to the Audio (mp3 format) as recorded by KTEP, Public Radio for the Southwest.
Contributor: Kodi R. Jeffery, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.
Female Brown-headed Cowbird. Photograph by Lee Karney, courtesy of the U.S. Fish and Wildlife Service.
Ligon, J. S. 1961. New Mexico Birds and Where to Find Them. University of New Mexico Press, Albuquerque, 360 pp.
