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Name: Jean C.
Status: educator
Age: 40s
Location: N/A
Country: N/A
Date: 1999-2001


Question:
My name is Jean Case and I teach second grade in a small town in South Dakota. We have a nest in a hanging flower pot outside of our classroom. It is a purple finch nest with small white eggs. A few days ago, we noticed that there was a new egg in the nest, but this egg is larger and has brown specs on it. Then, the next day we noticed that one of the finch eggs had disappeared. Today, we noticed another of the large brown speckled eggs. Can you please tell us what kind of bird this could be and why it layed eggs in the finch nest. Sincerely, Jean and second graders


Replies:
This is the description of brown-headed cowbird eggs from the Birder's Handbook: EGGS: White to grayish-white, marked with browns. 0.8" (21mm). (Copyright 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye.). Does it match? Cowbirds are nest parasites that lay eggs in the nests of other birds, sometimes ejecting a host egg at the same time. Apparantly they evolved this behavior in centuries of following buffalo herds on the prairies, which meant the cowbirds, like the buffalo, were constantly on the move, making conventional nesting difficult.

J. Elliott


This is very typical behavior of a parasitic species of bird. The most commonly known one is the Cowbird which lays large light brown to speckled eggs in the nests of other species. They have been known to kick out the other eggs to make room for their own. When the Cowbird chick hatches it is generally larger and more vocal than the chicks which belong in the nest. Because most parenting instincts of birds depend on the vocalization and open mouth image of the chicks, the Cowbird chick gets most of the food. When the Cowbird chick is strong enough, it will kick out any competitors. You can remove the cowbird eggs yourself so the remaining hatchlings will be care for properly. Don't worry about leaving your scent; it is an old wives' story. However, if the nest is disturbed too often the parents will abandon it. I have successfully observed hatchlings and parent care when I've limited nest visits to ten day intervals.

Cherie Breffeilh


Your unfortunate speckled finches are being parisitized by a cowbird. Cowbirds lay eggs in the nests of other birds because the other birds will do all the work of raising the cowbird chicks for them. To make matters worse for the host birds, the cowbird parents will, as you've seen, destroy the host birds's eggs, and so will the cowbird chick once it hatches.

So, you and your class may get the "privelege" of watching cowbirds reproduce at the expense of the purple finches. Nature is not always pretty.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois


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