Bewick’s Wren Outsmarts Cowbird

Cowbird Egg

One day last week I documented these Bewick’s Wren eggs in a nestbox at Dyess. I noticed one egg appeared slightly bigger. Was this an illusion or was it actually bigger? After perusing the internet for pictures of cowbird eggs, I came to the conclusion that this egg was a Brown-headed Cowbird’s egg. As everyone knows the cowbird is a freeloader in the bird world; they lay their eggs in other birds’ nests and then leave the rearing of that egg to the host family. Usually the cowbird hatches first, kicks the other eggs out of the nest, or hogs all the food and matures really fast. These scenarios prevent the song birds from raising their own kind. No wonder cowbirds are trapped and controlled where endangered species are at risk.

So today I was totally surprised to find only four eggs in the nest. The cowbird egg was gone. I did not remove the egg; no one else removed the egg. Conclusion? The Bewick’s Wren removed it. Let’s hear it for the wren!

2 responses to “Bewick’s Wren Outsmarts Cowbird”

  1. Hmmm. Are the Bewick’s Wrens nesting in a bluebird house, by any chance?

    I can’t imagine a Brown-headed Cowbird fitting into the entry hole in a normal wren house.

  2. Yes, Joe, they are. Twenty-seven nestboxes made according to the NABS’s (North American Bluebird Society) dimensions were installed in the spring of 2006. Not only are Eastern Bluebirds using the boxes but Bewick’s Wrens, Black-crested Titmice, and Ash-throated Flycatchers are taking advantage of the extra real estate. Oh, and one mouse tried to set up house but it was evicted.