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Simple things you can do to predator-proof your boxes. 

By Ron Kingston 

Picture a perfect farm scene, and it might include bluebird boxes on fence posts, or nailed to the old apple tree. I learned the hard way that both these classic methods of mounting nestboxes create potential deathtraps for bluebirds.  Ten years ago, my first bluebird boxes were nailed to trees in my yard.  All went well that first year, but the second year, the local raccoons and black rat snakes learned that an easy meal awaited them in my boxes, and a brooding female and several broods of young went to them instead of into the skies. 

Many people who have a number of bluebird boxes to monitor consider predation a natural part of the scene, which, of course it is.  But a distinction should be made between bluebirds that nest in natural cavities and those attracted to artificial sites.  How many times have you walked right past a woodpecker hole high in a tree and never noticed it? Can you say the same of a nestbox mounted on a tree, fence post or pole?  Now imagine you’re a grizzled old raccoon or black rat snake, veteran of many years of searching for birds’ nests hidden in almost every imaginable situation.  You know to watch for parent birds carrying food, to listen for or sense the shrill pipings of nestlings.  Just once, you follow these cues to a wooden box, and are richly rewarded for your climb – a meal and a package to remember, and the nestboxes in your territory become predator feeders. 

In attracting bluebirds away from cryptic natural cavities to conspicuous nestboxes, we are in a sense setting them up for predation.  The incubating female, potential mother to dozens of offspring, might slip unnoticed into a tree hole, but less secretly to a box out in an open field.  She is at special risk and her death impacts the breeding potential of local population.  Should we put up nestboxes at all? Yes, but only if we accept the responsibility that goes with them, to monitor and protect them from predators. 

As I continued to work with bluebirds, my learning curve continued to rise, albeit slowly.  Reluctant to take my boxes down, I took the easy way out. I put hole-mounted “predator guards” on the boxes, a 1-inch thickness of wood that effectively deepened the box entrance to 1 ¾ inches.  In theory, a raccoon would be unable to reach through this thickness and then down to grab the birds.  No one told the ‘coons, though, and if it was a little harder to get the reward, they simply kept at it, or chewed the guard off.  Needless to say, the snakes were unfazed.  I thought about the terror a mother bird must experience as a raccoon chewed its way through her door, and I decided that mounting a predator guard on a box hole is like putting an ambulance at the bottom of a cliff.  Once the predator is on the box, there’s very little hope for the bluebirds inside.   

Off came the boxes on the trees and fence posts. Out to the plumber’s supply to buy 8-foot lengths of ¾ inch (inside diameter) galvanized pipe, and strapping brackets to be screwed into the back of the boxes.  I settled on 30-inch conical sheet metal baffles, kept in place under the box with hose clamps above and below the baffle neck.  The predation stopped cold, and maintaining bluebird boxes turned from a guilt-fest into the pleasure it ought to be.

The big baffles had some drawbacks.  They had to be removed at the end of nesting season, lest they self-destruct in winter winds. The boxes had to be removed to take them off.  They were big and cumbersome.  Baffles made of plastics—even those sold as ultraviolet resistant—simply broke down in sun and freezing temperatures. 

I decided to run tests of other baffles.  I began setting table scraps out on a platform bird feeder, and soon raccoons were coming nightly.  They climbed the galvanized pipe with ease.  Grease did nothing to stop them, for it soon hardened and got sticky.  (Even fresh grease won’t stop snakes).  PVC pipe was easily climbed; they simply gave it a bear hug and shinnied up.  The same went for a cedar post wrapped with sheet aluminum.

Finally, I found a baffle that worked, that was easy and cheap to make, and didn’t have to be removed. It’s just a 36-inch section of galvanized stovepipe, 8 inches in diameter.  For roughly $8.00 you can ensure nesting for bluebirds, and disappoint raccoons, snakes, cats, opossums, chipmunks, and mice. It should be mounted just under the box. 


Materials used: galvanized pipe ¾” in side diameter, strapping brackets and weather proof screw (to mount box to pole), hardware cloth (1/4” mesh), machine screws with nuts hanger iron (in two 7” strips), galvanized stovepipe (36x 8). 

With tin-snips, cut the hardware cloth into a circle 8 inches in diameter.  Place it over the stovepipe, bending the edges down so that it will fit snugly into the pipe, about an inch down from the top.  Close any gaps between hardware cloth and stovepipe otherwise snakes may squeeze through. 

Next, use tin-snips to cut three tabs in the top of the stovepipe.  Bend them over the hardware cloth.  Cut a small hole in the middle of the cloth to allow the assembled baffle to slip over the box-mounting pipe. 

Bolt the two strips of hanger iron securely on either side of the mounting pipe, and bend them to support the hardware cloth. Duct tape wrapped around the pole helps hold the hanger iron in place. Slip the assembled baffle over the hanger iron bracket, just below the nestbox.  It should wobble a little, which further discourages predators. 

Article from Bird Watcher’s Digest

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