For the Birds Radio Program: Chickadee vs. Wren
One of my neighbors had chickadees nesting in her bird house until House Wrens moved in.
Transcript
I got a phone call last week from a woman in my neighborhood who had chickadees nesting in a wren box in her yard. The chickadees had used the same box last year with great success, and so this year she was hopeful that the same thing would happen and was keeping track of the eggs.
When she last looked, two had hatched, and then the next day when she was out on her lawn she discovered tattered pieces of the delicate nest easily recognized by tiny pieces of mosses woven in. She looked inside the nest box in horror to find everything gone.
The nest has a tiny entrance hole too small for house sparrows to enter, and she was mystified about what had happened to the chickadee babies. That very day she’d started hearing a house wren singing in her yard. It’s ironic that the bird we most often set out boxes for is so shockingly rude to other birds, but these adorable and bubbly little wrens really do puncture holes in eggs and even in nestlings, toss them out and destroy nests of other cavity nesters as large as bluebirds.
People who run bluebird trails design holes to exclude starlings, and they toss out house sparrow eggs and can legally trap or shoot the sparrows, but when a house wren discovers the box there’s little to do to protect the poor bluebirds.
The woman in my neighborhood discovered the next day that the box was indeed filled with sticks, proof positive that a wren had appropriated the box for his own. Ironically it may still never be used to raise wren babies, a male wren takes over as many potential nest cavities as he can find on his territory, filling them with these stick nests, then the female chooses just one to use as the actual nest. In many places house wrens are the number one cause of nest failure for prothonotary warblers, chickadees, bluebirds and tree swallows.
How can we prevent house wrens from destroying nests of our own backyard birds? There’s no way we can predict what every single house wren will do, but we can improve the chances of bluebirds and tree swallows when we consider the probabilities. House wrens usually avoid nest sites greater than 30 meters from any significant woody vegetation, so placing bluebird and swallow boxes out in the open makes them less inviting to wrens. Wrens also prefer nesting fairly close to the ground, so setting boxes for chickadees and prothonotary warblers fairly high up in trees will help protect them from wrens. Unfortunately house wrens are functionally illiterate and haven’t read the research, there will always be individual house wrens that choose sites higher than the research indicates they should.
I haven’t found my own little chickadees nest cavity yet, I haven’t really been searching for it, but I do see George and Martha carrying mealworms to the highest part of a dead birch at the back of my neighbor’s yard, and so I’m sure that’s pretty much where the nest must be. I’m hoping the wrens in my yard honor the law of averages and limit themselves to cavities much lower to the ground. Seeing how bedraggled poor George and Martha are, flying constantly to and fro searching for food and feeding their little ones, I know I’d be devastated if they lost their chicks after all this. House wrens are lovely and endearing birds in their own right, but I’m afraid I’d be inclined to do violence if one hurt George and Martha’s little babies. I’m Laura Erickson speaking for The Birds.