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Name: Cynthia H.
Status: educator
Age: 50s
Location: N/A
Country: N/A
Date: Saturday, May 18, 2002


Question:
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. Any ideas??


Replies:
This sounds very suspiciously of a cowbird. Cowbirds are common in your area. The female always lays her eggs in other bird's nests and never raises her own chicks. 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 species.

Nature has some strange designs!

Steve Sample


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