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Dear Marion: What Can We Do About Aggressive Wrens Taking Over?



Dear Marion,

This spring we set up five bluebird houses with the hopes of enticing swallows and bluebirds to take up residence. We love watching their little families thrive and also enjoy their voracious appetite for mosquitos! Last year we had two swallow families nest on our property and the mosquito population thankfully went way down.

Unfortunately this year the wrens have staked their claim on two of the houses and a chickadee family in the other. We did try to thwart their efforts by taking out the nest almost daily but they were relentless and kept starting over. We gave it up to them because it looked like they desperately needed to nest and lay eggs.

My question is, should we have continued to keep them away because they are known to be aggressive to other birds? Or did we do the right thing? Also, what can we do to entice bluebirds and swallows to the houses beyond just putting them up? Is there something more we can do? Your advice to avoid this issue next year will be greatly appreciated.

Daina

Hi Daina,

First of all, congratulations on setting up nesting boxes for needy bird species. We could all take encouragement from your efforts and add nesting boxes to our properties.

For birds such as bluebirds and tree swallows, only cavities will meet their nesting criteria. There are less natural cavities available every year so artificial cavities, such as nesting boxes, are vital for their breeding success. Unfortunately, our native house wren also finds these nesting boxes quite appealing. The dividing line is that these boxes are NOT crucial for wrens to nest successfully.

Usually, we discourage wrens from nesting in our man made boxes so this leaves boxes free for our needy bluebirds and tree swallows. Once wrens get hold of our boxes they dominate the whole area by, not only using a box for their own needs, but by placing dummy nests in surrounding boxes. This allows the wren family to have domination over a certain territory and eliminates the birds we are trying to help.

I know this sounds mean, but we have to be persistent in clearing our boxes of wren nests because they are an aggressive bird. Not only will they fill up surrounding boxes with dummy nests, making them unusable for bluebirds and tree swallows, but they will eliminate birds that try to use these boxes by poking holes in eggs and tossing them out of the boxes. Sometimes they will even injure chicks and parents.

Unfortunately, if the wrens have successfully fledged chicks from your boxes, they will be even more persistent now that they have had breeding success. There are 2 actions available to you. Relocate these boxes so that they seem less appealing for wrens and double your efforts at wren eviction next year. Your efforts will be rewarded eventually when tree swallows and bluebirds take up residency.

There is nothing more rewarding than having your morning coffee and watching all the bird activity at your nesting boxes.

I am hoping this helps.

Yours in conservation,
Marion Robertson.

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Marion Robertson

Marion is co-owner of Bee Sweet Honey Co and Puslinch Naturally Native Trees

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