Name: Cynthia H.
Date: Saturday, May 18, 2002
We monitor blue bird houses at a nature preserve here in
Niles, MI (close to Indiana border).
We are very familiar with the eggs of the blue bird,
sparrows, wrens and tree swallows who also like the houses,
but today we discovered eggs in two of the houses that have
us mystified. The eggs were much larger than blue bird eggs
and were robin's egg blue. The hasty grassy nest was just a
few inches tall and one was lined with what looked like blue
jay feathers. We cannot think of any cavity dwelling birds
that could get into the 1 1/2 inch hole in the bird house.
This sounds very suspiciously of a cowbird. Cowbirds are common in your
The female always lays her eggs in other bird's nests and never raises her
If the egg was larger and somewhat close in color, I would suspect this
species. The cowbird
female will even come close to matching the color of the eggs of the host
species. A cowbird
egg will hatch first, the chick will stretch to remove all the other eggs
from the nest, and become
the sole surviver. The surrogate parents will attend to the chick just like
it was their own, and the
chick will fledge knowing it is a cowbird and not the surrogate parent's
Nature has some strange designs!
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Update: June 2012