Bluebirds are a beloved songbird that many people enjoy having in their yards. However, the territorial and aggressive house wren can often take over bluebird nesting boxes, damaging eggs and killing nestlings. This leaves bluebird enthusiasts wondering how to deter wrens while still attracting bluebirds. There are several methods you can try to make your bluebird house wren-resistant.
Why are wrens a problem for bluebirds?
Wrens and bluebirds often compete for the same nesting cavities in backyards. Wrens typically return from migration and begin claiming nesting sites in early spring, before bluebirds arrive. Once wrens take over a nest box, they will defend it aggressively, even destroying bluebird eggs and killing nestlings.
Wrens are persistent and will continue to harass bluebirds that try to claim a nest box. They may peck holes in bluebird eggs, remove nesting material, or even kill hatchlings. This poses a real threat to local bluebird populations struggling to find safe nesting sites.
How to make a bluebird house wren-resistant
Here are some tips for deterring wrens from your bluebird boxes:
Use a larger nest box hole
Bluebirds prefer a 1.5” diameter entrance hole, while wrens can only use an opening 1.25” or smaller. Look for bluebird houses specially designed with the larger hole size. You can also alter existing nest boxes by enlarging the entry hole.
Place boxes in open areas
Wrens prefer dense shrubs and woodland edges. Bluebird boxes will have a better chance if placed in open fields or spaces at least 30 feet from trees and shrubs. Mount the box on a pole in the center of the open area.
Use wren guard cones
Attach a plastic or metal cone below the entry hole to prevent wrens from accessing the box. The cone should be at least 8 to 10 inches long with a 2 to 3 inch opening at the bottom. This allows bluebirds to drop down into the box but deters wrens.
Coat the inside of the box with vegetable oil
Wrens don’t like slippery surfaces. Apply a light coat of vegetable oil on the inner walls and floor of the nest box. This won’t harm bluebirds but prevents wrens from getting secure footing. Reapply occasionally through the season.
Hang multiple bluebird boxes
Try putting up several bluebird boxes rather than just one. Space boxes at least 300 feet apart. This gives bluebirds more options to potentially claim a nest site before wrens occupy all the boxes.
Add a wren box nearby
You can attempt to appease territorial wrens by putting up a dedicated wren house about 100 feet from a bluebird box. The wren may claim the wren-sized box and leave the bluebird house alone. Just be aware they may still harass bluebirds in the area.
Remove wren nests ASAP
Check nest boxes weekly through spring. Promptly remove any wren nesting material as soon as you notice it. Wrens build dummy nests in boxes to claim them, so disassemble these before they finish nesting. Removing completed wren nests with eggs or young is controversial, so use your best judgement.
Clean out the box in fall
At the end of the season, clean out old nesting material. This gives bluebirds a clean start come spring before wrens can build nests and claim the site.
When to remove wren deterrents
It’s important to remove any wren-proofing once bluebirds have successfully begun nesting in the box.
Take off wren cones, clean off vegetable oil, and open any blocked holes. These deterrents could interfere with the bluebird parents coming and going to feed their young.
Check that bluebirds have accepted the box before migrating south in the fall. If wrens take over a box, reapply deterrents to prepare for the following spring.
Monitor nest box frequently
Keep a close eye on any nest boxes through spring and early summer. Weekly monitoring lets you promptly remove wren nests and identify if bluebirds have claimed the site.
Watch for activity at the box entrance for clues that wrens or bluebirds are present. Use a flashlight to carefully check the interior contents without disturbing the birds.
Track your observations of bird activity and nesting progress. Detailed records help inform your nest box management efforts.
When to give up on a problematic nest box
In some cases, wrens may persistently claim a nest box year after year. They can be remarkably determined in returning to a prime site.
If you’re unable to successfully deter wrens after several seasons, it may be time to accept defeat. As frustrating as it is, the wisest option is often to move the nest box somewhere else on your property.
Look for the most wide open location possible, at least 150 feet from the original problem site. Keep monitoring and trying different deterrents at the new box.
Alternative nesting options for bluebirds
Rather than battling wrens, another approach is providing alternative nesting sites tailored to bluebirds. Consider these options:
– Hanging multiple bluebird boxes at ideal open locations around your property.
– Installing bluebird nesting tubes or boxes on metal fence posts or poles away from trees.
– Placing woodduck boxes with sloped, rough inner walls that bluebirds can grip but wrens can’t.
– Erecting bluebird boxes with slotted openings instead of circular holes.
– Putting up gourd-style nesting chambers mounted on poles.
The more choices you can offer, the better chance bluebirds have of finding a safe spot. Provide nesting habitat in adjacent yards and properties where possible.
Partnering with neighbors
Join forces with neighbors to make your area as bluebird-friendly as possible.
Work together to put nest boxes in optimal spots over a wider area. This gives bluebirds several suitable nesting locations away from wren territories.
Share observations and information to enhance monitoring and deterrence. A coordinated community effort is extremely beneficial.
Educate each other on properly managing and cleaning boxes. Consistent nest box care from season to season maximizes nesting success.
Landscaping to support bluebirds
Your yard’s landscape can also promote or hamper bluebirds in the neighborhood. Here are some tips:
– Allow dead trees to remain standing, which bluebirds use for perching.
– Maintain mowed grassy areas up to 50 feet around nest boxes.
– Eliminate dense brush piles where wrens like to lurk.
– Plant some seed and berry producing native trees and shrubs.
– Avoid using pesticides which reduce insects bluebirds feed on.
– Provide a water source like a birdbath or fountain.
– Limit the number of feeders, which can draw wrens.
Dealing with house sparrows
Along with wrens, invasive house sparrows can also compete with bluebirds. Sparrows are aggressive and will take over nest cavities.
Similar wren deterrents can help make boxes sparrow-resistant. Monitor boxes diligently to remove sparrow nests before they contain eggs.
Trapping unwanted sparrows is controversial but often necessary. Use specially designed traps cautiously and only target problem house sparrows.
Enjoy the rewards
With some diligence and the right habitat, attracting bluebirds while deterring wrens is very achievable. Focus efforts each spring, then enjoy watching bluebird families successfully raise young.
The beauty of bluebirds gracing your property will make the effort well worth it. Their presence indicates a healthy native ecosystem. Better understanding bird behavior also connects you with the natural world.
Reward yourself by recording the antics of baby bluebirds in the nest or spotting fledglings trying out their new wings! Protecting bluebirds from wrens takes commitment but pays off.
Conclusion
Coexisting with competitive, aggressive birds like wrens is one of the challenges of bluebird conservation. A variety of nest box adaptations and habitat improvements can tilt the odds in the bluebird’s favor. Being vigilant and actively managing nest sites makes a big difference. Getting neighborhood support and using multiple strategies bolsters success. With some patience and persistence, you can achieve your goal of hosting bluebirds in your yard. The joy of watching these special songbirds raise young will make it all worthwhile.
