Bird Watcher's General Store

House Wrens Throw Out Birds and Eggs

Dear Bird Folks,

We have a family of bluebirds in one of our birdhouses. They have been fun to watch, until this morning when we found four newly hatched bluebird chicks laying dead on the ground below the house. We looked for signs of trouble, but everything seems fine. Any idea what happened?

Ė Marjory, Brewster, MA

To begin with, Marjory,

Iím sorry to hear about your little bluebirds. The adults will likely re-nest, but itís still no fun to find dead baby birds. Iím also sorry if I spelled your name wrong. After we ended our conversation, I realized that I had neglected to ask for the proper spelling. But then I thought, how tricky can Marjory be to spell? Well, it turned out to be very tricky. I found lots of options: Some versions have Js, some have Gs and still some are without Ys altogether. When all of you Marjory, Margery, Marjorie folks come to a consensus, get back to me and Iíll make any needed corrections.

For years, Blue Jays have gotten a bad rap for eating other birdsí eggs. While itís true that jays will occasionally eat an egg or two, so do a lot of creatures, including most of us. Jays might even take small nestlings, if given the opportunity. But I doubt very much they were the villains in this case. It would be just too difficult for a jay to grab any bird if it was safely curled up inside a birdhouse. However, your birdhouse offers no protection from raccoons or those dreaded housecats. With their long legs and claws, either creature could easily reach into a house and drag out its contents. And while raccoons can be a problem for baby birds and cats are a massive problem for birds of any age, neither is guilty this time. When cats and raccoons strike, telltale nesting material is found sticking out of the hole or on the ground below. You said that you found no signs of trouble, so both animals are off the hookÖonce again, this time. Surprisingly, snakes are another problem. More than one person has opened a nest box and discovered a snake staring back at them. Fortunately, that hasnít happened to me. If it had, you would have found me passed out on the ground right next to the baby birds.

Other possible perpetrators include red squirrels, chipmunks, mice and the list goes on. There are countless creatures that are more than willing to make a meal out of baby birds. But hereís the thing: Your tiny bluebirds werenít eaten, they were just dead on the ground. This piece of info puts the spotlight squarely on an unlikely suspect. Many folks donít like to admit it, but the House Wren, a spirited and popular backyard bird, has a real dark side. With its bubbly song and energetic antics, the wren is fun to watch, but it also has serious control issues. It doesnít like having neighbors and will often fill nearby birdhouses with twigs in order to prevent any other bird (chickadee, titmouse, bluebird, etc.) from moving in. If it finds a nest that has already been built, the psycho wren will actually remove the nest, bit by bit, like a tiny repo man. And it gets worse. When a wren discovers another birdís eggs, it will make sure they never hatch. How does it do that? It just pierces the shells with its sharp beak and thatís the end of that. Now comes the ďdonít lookĒ part.

Filling an empty box with sticks, physically removing an active nest and destroying a neighborís eggs are all bad, but House Wrens (which should not be confused with their less troublesome cousins, Carolina Wrens) have an even uglier trick up their feathered sleeves. If the little egg-piercer finds eggs that have already hatched, it carries out an even more dastardly deed. The wren will, on occasion, grab the helpless chicks and toss them out of the box and onto the ground below. This appears to be what happened to your bluebirds. The obvious question we should be asking is, why? Why would the wren do that? Is it about food competition? Is there some territorial advantage to be gained? These are the questions researchers have been asking for years. After several lengthy studies, and after weighing all the evidence, researchers have come to the conclusion that House Wrens are just jerks. There is no other possible explanation.

It should be pointed out that House Wrens arenít only mean to bluebirds. They hate all of their neighbors equally, including other wrens. In addition, this isnít totally a macho thing; the females are just as nasty. The next question is: Can anything be done to stop them? Not really. There are a few tricks you can try, but the effectiveness is somewhat limited. Also, House Wrens are native songbirds and thus are afforded the same legal protection given to robins, cardinals, hummingbirds, etc. Sometimes itís hard to understand the ways of nature, but we arenít the bird police. This behavior has been going on for centuries, and while itís upsetting for us to see, the birds will work it out. They always have. Besides, we humans have our own abhorrent behaviors we probably should focus on solving first.

Once again, Iím sorry to hear about your little bluebirds, Marjory, Margery, Marjorie, but as I said, the adult bluebirds will most likely re-nest somewhere nearby. And whether you like it or not, you have a family of House Wrens living close by as well. You should look for them. Wrens are actually fun to watch. Just donít get too close. RememberÖtheyíre jerks.

Artwork by Catherine Clark

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