Up Up and Away: The Elevator Post

by Paul Chance

An important factor in bluebird propagation is loss to predators.  Cats have been known to crouch beneath nesting boxes and pounce upon adult birds when they prepare to enter the box.  Snakes and other predators climb posts to get at eggs or chicks.

One way of reducing these losses might be to raise the height of the box. Zeleny reports that bluebirds will occupy boxes 15 feet (4.5 m) or more above the ground.  Unfortunately, boxes more than 5 feet (1.5 m) high are difficult to monitor and maintain.

I have devised a simple method for putting boxes at heights of 7 feet (2.1 m) or more that nevertheless makes them easy to monitor and maintain.  The system uses two 5-foot sections of PVC plumbing pipe [one 1.5 inches (3.8 cm) in diameter, the other 2 inches (5.1 cm)] and a 10penny nail.

To construct an elevator post, insert the narrower pipe (the post) into the wider one (the shaft) so that the bottom of the post is about 1 foot (0.3 m) below the top of the shaft.  Now drill a 1/4 inch (0.66 cm) hole about 2 inches below the top of the shaft such that you can fit the nail through the center of both pipes (see Figure A).  Remove the post from the shaft and attach the box near the top of the post.  Wedge a bit of hardware cloth into the top of the post to prevent birds from exploring and becoming trapped in the pipe.

Figure A

Figure B

Put the shaft into a hole in the ground so that the bottom of the shaft is about 2 feet (0.6 m) below the surface.  Now insert the post into the shaft.  At this point the top of the box is about 4 feet (1.2 m) above the ground.  The box may be raised by lifting the post 3 feet (0.9 m) and then sliding the nail through the 1/4 inch holes.  The nail keeps the post from sliding down the shaft.  The box is now about 7 feet above the ground (see Figure B).  

To inspect or clean the box, remove the nail with one hand while holding the post with the other, then let the post slide slowly into the shaft. it is important not to let the post slide of its own accord, since any birds in the box might be injured when the post stops abruptly.

If vandalism is a problem, the nail may be replaced with a bolt and nut.  If the nut is tightly secured, pliers are required for It’s removal and this should discourage miscreants.

The only difficulty I have had in using the elevator post is in aligning the holes in the shaft and post when inserting the nail.  This problem can be dealt with by aligning the holes and then marking the shaft and post with indelible ink or an exterior paint.  A cross, drawn so that it overlaps shaft and post, will indicate both the vertical and horizontal positions of the holes.  When the two pipes are arranged so that the cross is intact, the holes are aligned.

Five-foot sections of pipe result in a maximum box height of about 7 feet.  Greater height may be obtained with longer sections of pipe, but it should be kept in mind that this raises the center of gravity and the vulnerability of the box to wind.  It seems likely that a 7-foot height is sufficient to put the box out of the reach of most four-footed predators.

I have used this system for about four years without problems, but my experience has been that bluebirds prefer boxes 4 to 5 feet above the ground.  The elevator post is of little value if bluebirds do not use higher boxes.  It may be possible, however, to "persuade" bluebirds to nest at safer elevations than is their want.

The idea (which I have not put to the test) is to place boxes at 5 feet using the elevator post described here and then, once the box is occupied by bluebirds, raise the box gradually.  This can be done if holes are drilled through the post 6 inches (1 5.2 cm) apart.  Every two or three days, remove the nail, raise the post 6 inches, and reinsert the nail.  The box should soon be out of the reach of most predators.  The question of how rapidly the box may be raised without inducing the birds to abandon the nest remains to be answered, but in the absence of research evidence to the contrary, a slow "ride to the top' is recommended.

The elevator post is inexpensive, durable, and easy to build and use.  I believe it may substantially reduce predation, and I hope some birder will test that hypothesis in a systematic way.

1 also hope birders who try the elevator post will let me know what results they obtain, and what problems they encounter.  In addition to the address below. I can also be reached on the internet:  INTERNET: 72134.1263@compuserve.com

P.O. Box 248
Laurel, DE 19956