Birds and Different Eggs
Name: Nancy A.
Date: Saturday, May 18, 2002
A small brown bird has made a nest near our back door here in north
eastern Illinois. I have not gotten a good look at it because it flies
off when it hears the door open. It has laid 2 or 3 tan eggs with brown
speckles. However, this morning I also noticed 3 more light grayish blue
eggs as well. I believe I remember learning that certain birds will be
interlopers, and lay their eggs in others' nests, hoping that their
progeny will survive over the original nestlings. Is this true? What
sorts of birds exhibit this kind of behavior? Is it common? My kids (10,
8, and 5) are scandalized at the thought of the original babies not
getting their mom's full attention! I explained that birds do not think
in the same ways as people, and that nature sometimes may seem cruel to
them, but I would love to give them more information. I have scanned the
Internet, and have not found anything. I would love for my kids to gain a
real passion for learning about birds. I am hoping this will spark their
interest further. Thanks so much for your help and information. What a
terrific service you provide!
Yes, there is such a bird in Illinois. The Common Cowbird female does
exactly what you have suspected. The female after mating will observe nest
building of another species and lay one egg in the same nest when the other
birds are occupied elsewhere. The eggs she lays will (to the nest owners)
look like thier own. However, during incubation, the cowlbird eggs will hatchfirst.
The large cowbird chick is accepted by the surrogate parents and the chick
will remove, by a stretching-liken behavior, the other eggs in the nest so
it is the only one present. It gentica,ly knows it is a cowbird and will stay with
the parents it has for as long as it needs, fled (leave) and never return. The
surrogate parents do not know that difference.
There is usually only one cowbird egg per nest. I am sure there may be
For the most part, all birds are born with the behaviors it needs to
survive. This is
one of many examples of how a species survives successfully. There is no
that I have read that would indicate that the Cowbird does damage to any
man does all of that all by himself!
If you haven't already, puchase a Bird Identification book to learn about
which birds you
may see around your house. In Northeastern Illinois during the spring, a
birdwatrcher may see over 120 different species of birds in a few hours
(early to mid May).
Here are two informative links I found using the Newton search engine:
If the host birds understood what was happening, chances are they would be
more upset than your children are. After all, it is their resources that are
going to another species at the expense of their own reproduction.
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
The only nest parasite of the U.S. is the brown-headed cowbird; Some
European cuckoos are nest parasites, but American cuckoos are not. Cowbirds
probably developed parasitism as they evolved following buffalo herds on the
great plains and thus did not stay in one place long enough to build their
own nest. For more information about cowbirds, try this site, type in the
name in the search window and you will get a page with good basic
information, and on the page will be a link to the text on cowbirds from the
A.C. Bent books, Life Histories of North American Birds, originally
published by the Smithsonian. Those books are old so much information has
been updated but they are incredibly detailed.
Another birding site of interest is
Audubon Society has a bird page with links:
And you can find many more with a little searching. Encourage your kids to
understand, as you have started, that while we should not expect wild
creatures to behave the way we do, sometimes wild things do need our help.
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Update: June 2012