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Master Gardener Journal  

C R E A T U R E   C O M F O R T S

Building Nestboxes: Design & Location are Key

by Sue Hakala,
Master Gardener

There about 650 different bird species in North America, with only about 86 nesting in cavities. Woodpeckers are primary creators of nest cavities. Other cavity makers include lightning, insects, fungal infections, and plant diseases. Unfortunately, in the home landscape we humans tend to tidy up these things, thus, eliminating potential nest sites. It is helpful to birds if we replace them.

Cavity nesters have less of a chance of their young or themselves being preyed upon. The cavity also provides protection from the elements and parasitism by cowbirds. Fledging success is 60 to 80 percent higher for cavity nesters than for open nesters.

There are only certain species that will ever use a nestbox, so don't think that just any bird will move in. It will have to attract species that have evolved to investigate dark holes, something open-nester species will never do. Introduced birds, such as house sparrows and starlings, are very aggressive in defending a nestbox and throwing out birds that you might want to attract. It's best to develop the attitude that attracting any birds to your nestbox is wonderful.

The key to success is the box design and location. It is important to think like a bird. Birds like a protected area with trees and bushes around. Sturdy construction of the nestbox is essential. Use untreated wood that is at least 3/4 - inch thick; to more closely resemble a tree cavity. Natural cavities are rough on the inside--something birds like. If the house you make or purchase is smooth on the inside, file, rasp and gouge it so that the birds can have footholds to hang on to. Cutting a series of horizontal grooves below the entrance makes it easier for the babies to have something to climb up on when it is time to fledge.


Never use treated wood, as the chemicals can leach out and harm the babies. Also, do not paint or in any way treat the inside of the house, as the babies may ingest the stuff and die. Don't use a house that has been glued or stapled.

Never use insect repellent on the nestbox, as the fumes can kill the adults and the babies. Do have a roof that overhangs the sides by about 5 inches to provide shade and shelter from rain. Do not have an outside perch, as it just gives larger predators who can't fit through the entrance hole a comfortable place to stand while trying to get the babies. Natural nest cavities do not have perches for this reason. House sparrows prefer nestboxes with perches. Entrances should be at least 3 inches above the house floor to make it harder for predators to reach in and have a meal.

The size of the entrance will narrow down the kinds of birds that will use the house. For instance, wrens like holes that are smaller than 1 1/8 inches. About 12 species of cavity-nesting birds will use a house with 1 1/2-inch openings. Woodpeckers and flickers like entry holes 2 1/2 inches in size.

Site your nestbox so that it faces away from prevailing winds, and so that predators can't get at it. Tree mounting is not a good idea, as it provides easy access for a variety of predators. Hang or install the nestbox on a pole. This may mean that you will have to devise some kind of baffle to keep out squirrels, house cats, snakes, and others. Install a 30-inch long metal sleeve on the pole about 6 feet above the ground so the predator can't jump over it. You can also use an inverted metal cone directly under the nestbox to discourage raiders. If ants are a problem, apply grease mixed with a little turpentine (to keep the grease from drying out) on the pole at least 6 inches above the ground so nothing will rub it off.

Be certain that your house has several small holes drilled in the bottom for drainage. Also, place a few small holes high up on the sides for ventilation. Keep these holes small to keep out predators.

You may be tempted to clean out the house after the babies have fledged, but it may not be a good idea. Research is showing that birds prefer to use an existing nest, even if it isn't theirs. Birds have a higher success rate in rearing babies who are larger in size when using existing nests as a starter. Larger size equals greater survival success.

If you do prefer to clean your nestbox, make sure that your design includes a side panel that can be opened for you to do this. Remember not to use chemicals on the box. For your own safety wear rubber gloves and something to protect your face as the fine dust may cause an allergic reaction. Hantavirus may be present in nests of raptors (from the decomposing carcasses).

You might enjoy the fun of keeping records of your bird family. You can assist researchers by sharing your data. Contact the Cornell Laboratory of Ornithology, at the address below, and request North American nest-record cards.

Make your nestboxes even more attractive to birds by planting plants that provide safe perching places and food supplies nearby. Keep clean and fresh water available along with birdseed. Birds do just fine without our providing food and water, but it does help make their lives just a little easier, especially during the demanding nesting season.

There is a nationwide movement to place nestboxes on the back of highway signs to open up more territory for cavity nesters. Contact Hawk Mountain Sanctuary (address below) to see how you can be involved.

Cornell Nest Box Network
Cornell Laboratory of Ornithology/CNBN
P. O. Box 11
Ithaca, NY 14851-0011

Hawk Mountain Sanctuary
R. R. 2
P. O. Box 191
Kempton, PA 19525-9449

Maricopa County Master Gardener Volunteer Information
Last Updated January 25, 2003
Author: Lucy K. Bradley, Extension Agent Urban Horticulture, University of Arizona Cooperative Extension, Maricopa County
© 1997 The University of Arizona, College of Agriculture and Life Sciences, Cooperative Extension in Maricopa County
Comments to 4341 E. Broadway Road, Phoenix, AZ 85040,
Voice: (602) 470-8086 ext. 301, Fax (602) 470-8092