Gardening for Wildlife

Nesting box

Related Terms: nesting box, bird box, how to, installation, building a bird box

Approximately twenty-five Canadian bird species nest in the cavities of decaying trees. For many reasons, nesting sites are becoming harder to find, so these birds must settle for surrogate homes. A nesting box can be a real bonus for birds that rely on these cavities to raise their young. Some species, like the eastern bluebird, have declined seriously. One reason is the dwindling number of natural cavities available to them. In some areas, small pockets have been able to hang on because of nesting box programs organized throughout their range.

This nesting box will appeal mostly to bluebirds or tree swallows, depending on where you place it. You can adjust it to attract other birds by varying its size and the size and height of the entrance hole according to the accompanying table.

To create this nesting box you will require a single one-by-eight piece of lumber and 1.5-inch (4 cm) wood screws. Use wood that resists weathering, such as cedar, pine, or redwood, but not pressure-treated lumber because it can be toxic to wildlife. Scrap pieces of lumber, if the right size, are also suitable.

how to | installation | maintenance

 How to:
Cut the pieces as illustrated. The entrance hole must measure 1.5 inches (4 cm) in diameter and be 6 inches (15 cm) above the floor. Pre-drill screw holes to prevent splitting the wood.

Attach the sides to the back. Check that the roof sits flat. Place the floor flush with the sides and attach. Position the front panel as shown, securing with one pivot screw on each side. Check the movement of the hinges, then add the securing screw - the screw you will remove to clean the box. Then attach the roof.

Drill a few small holes (1/4") in the floor near the walls for moisture drainage and sand any rough edges. It is better not to paint or stain the box. If you do paint the box, use colours birds are attracted to - dull green or brown - and leave the interior, and the area around the entrance hole, in its natural state. Avoid lead-based alkyd paints and wood preservatives as they can be toxic. Pure linseed oil is a good choice to help preserve the outside of the box.

Do not attach a platform or perch outside the box. This will only obstruct the bird's entrance and encourage predators to raid the box.

Nesting Box Dimensions

Installation

Erect the box as soon as you spot your first dandelion or if you spot a tree swallow or bluebird. Putting it up too early will only encourage pest species such as the House Sparrow and European Starling to take ownership of your box. These introduced species, which are aggressive and often drive off our native species, don't require our help to survive.

Place the nesting box in a spot that gets some sun and turn the entrance away from the direction of wind and rain.

For bluebirds, place nesting boxes on 5- to 6-foot (1.5-1.8-m) poles in quiet, open fields, orchards, or pastures with some nearby trees or wires. Leave a minimum 300 feet (about 100 m) between boxes.

For tree swallows, situate boxes on 5- to 6-foot (1.5-1.8-m) poles in backyards, front yards, near fields, a river or pond. (This species will possibly use boxes on the sides of buildings or under eaves.) Leave about 50 feet (15 m) between boxes or make sure they are not visible to each other.

Metal poles are the best choice for mounting nesting boxes as it prevents predators from accessing the box. They should also be placed at a sufficient distance from trees and other structures so that squirrels and cats cannot jump to the box.

An alternative is to use a wooden post but slip a length of PVC piping around the post to prevent predators from climbing it.

Mounting nesting boxes on trees leaves the nest more vulnerable to predators. If you are placing the box on a tree be sure to install a predator guard. These tree guards help protect the nest while also providing a good place for bats to roost. See Hot Under the Collar for more information.

Make sure that your box is mounted securely. You don't want the first heavy rain or windstorm to blow it down wreaking the house and possibly killing any resident nestlings.

Maintenance

Take down and clean the box in the fall and, for bluebirds, between broods to rid it of parasites. It's a good idea to wear a face mask (available at hardware stores) to avoid breathing fungi and parasites. Scrub your box with a stiff brush and pour boiling water through it for disinfecting purposes. Allow it to air dry thoroughly in the sun if possible.
Leaving the box up all winter will encourage mice to take over uncleaned boxes or allow pest species to move in before migrant birds return in the spring.

Check on a regular basis that the structure is in good repair. In the fall, once inhabitants have left, you can take it down to repair a loose roof, warped bottom, or cracked side.
If damage occurs to the box during the nesting season, make repairs only when essential. Plan your moves and be quick. If you must remove the nest and eggs or young, remove the whole nest, make the repairs, and move away so the parents can come back quickly. Do not handle the eggs or young birds unless unavoidable and if so wear gloves and wash up right after.