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bluebird nestlings hatching.  Photo by Cher Layton  

If you never check your birdhouses, you're missing all the fun, and might actually be harming the birds you've invited to nest. More....

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- by E.A. Zimmerman

Many people who love nature and wildlife put up houses for birds.  Native cavity-nesting birds need safe homes to raise their young.  Bluebirds, Tree Swallows, chickadees, titmice, nuthatches, House Wrens, American Kestrels, and flickers are all local cavity-nesting birds that will use manmade nestboxes of varying sizes.

Monitoring is fun!  Bet Zimmerman checks out a nestbox.
CAPTION: Bet carefully checks what is going on inside a bluebird house. Monitoring is interesting, and helps ensure that the occupants live to fill the skies with blue. The box in this photo is an experimental bluebird nestbox, which is a combination of a Gilwood and a Troyer design. Photo by Doug Zimmerman.

Since 2003, Doug and I have fledged more than a thousand birds from nestboxes in Woodstock.  That number includes 270 bluebirds, which were becoming uncommon due to loss of habitat, pesticide use, and deadly competition from alien House Sparrows and Starlings.  The reasons our boxes successfully fledge so many birds are: 1) they are properly designed, 2) they are mounted on poles with wobbling baffles to prevent predation by raccoons, cats, snakes, etc., 3) we don't ever let House Sparrows use boxes, and 4) we monitor regularly.

Unfortunately, a lot of people put up nestboxes and forget about them.  They do not maintain or check them periodically.  Some are afraid of disturbing the inhabitants.  Actually, bluebirds are quite tolerant of humans.  Despite what your mother told you, they will not abandon their nest because you take a quick peak inside their house once a week.  In fact, if they could thank you, they would.  Here’s why.

  1. If you don’t look inside, you’re missing most of the fun!  You never know what you will find when you open a box.  Both young and old alike can enjoy witnessing the wonders of nature.  You will learn what birds use to construct their nests, discover tiny eggs, or maybe even have an opportunity to see a baby bird hatching.  
  2. Bad things can happen in boxes that are not monitored – See #3-10.  These things can harm and even kill the very birds you are trying to help.
  3. House Sparrows were introduced by humans, and are a Bluebird’s worst avian enemy. They often take over boxes that are not monitored.  House Sparrows attack and destroy eggs, nestlings and adult native birds.  By monitoring regularly, and taking other steps, you can prevent them from breeding in your boxes.  See www.sialis.org/hosp.htm for more information.
  4. Paper wasps or bees often invade boxes. Their presence will deter nesting altogether.  Wiping a thin layer of Vaseline or rubbing Ivory soap on the interior roof of the box will help keep paper wasps out.
  5. Mice can take up residence.  Small birds will not use a nestbox that has mice in it.
  6. You may think your box is sending beautiful baby birds out into the world, when in fact it is only providing Happy Meals for raccoons, snakes and outdoor cats. If you find out there has been a problem with predators, you can do something to prevent it from happening again.
  7. Territorial House Wrens may fill up boxes with sticks, to create “dummy” nests which they don’t actually use, making the house unavailable to other birds.
  8. Bad things can also happen to boxes that are not maintained.  For example, wood can rot or crack, allowing chilling rain to wet and kill nestlings.   
  9. Squirrels or Woodpeckers may enlarge the entrance hole.  A hole larger than 1.5” in diameter allows Starlings and other predators access to eggs and babies.
  10. Boxes that are not cleaned out at the end of the year can get so stuffed with leftover nesting material that birds can no longer use them. Or the next nest will be so high that predators can easily reach inside to nab eggs or babies.   

Checking a birdhouse is pretty simple.  Just walk up to it in the afternoon, tap on it and whistle or call out to let the bird know you’re there.  Then stand to the side and open the door, in case a parent is inside and wants to fly out.  Take a quick look for problems like paper wasps, and check for eggs or babies without disturbing them.  Then securely close the door and walk away.  Once the babies are covered with feathers, you should not open the box anymore, as they could jump out before they are ready to fly.  After the babies leave the box on their own, put a plastic bag over your hand and remove the used nest.  Then the box will be nice and clean and ready for new occupants. 

Monitoring only takes a minute but can save the lives of birds you have invited to nest in your box.  It will greatly increase the odds that your birdhouse is actually doing some good.  For more information on what you can do to help native birdhouse birds survive and thrive, visit www.sialis.org

Bet Zimmerman is a Certified Environmental Professional, and a Board member of the North American Bluebird Society.  She and Doug maintain 100 nestboxes in Woodstock, CT.  Visit her educational website on bluebirds at www.sialis.org.


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Originally published in the Villager newspapers on May 7, 2010


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