There's a serious shortage of accommodations in the bird world these days. About 24 Canadian bird species nest in natural cavities such as holes in decaying trees and stumps, but it's getting harder for them to find lodgings. Many potential homes are cut down for firewood or blown down in storms. Hectares of forests and woodlands are bulldozed to make way for subdivisions and other developments.
Nesting boxes around your property will be a real bonus for birds that raise their young in cavities. Many of these species settle comfortably into human-made dwellings. Some species, like the eastern bluebird, once faced serious decline because of the dwindling number of natural cavities available to them, but rebounded because of nesting box programs organized throughout their range.
- To cut material costs, try building with leftover lumber, or use any wood that resists weathering. Softwoods, particularly pines, are easy to work with. Avoid hardwoods, poplar, and basswood as they weather poorly. Lumber stock at least 2.5 cm thick will do. Create a natural log effect by using bits and pieces of wood with bark still attached. These slabs are less expensive and can be found in most sawmills and lumber yards. Never use pressure-treated lumber, as it can be toxic to wildlife.
- The location of the bird box - its dimensions, the size of the entrance hole, and the height of the hole from the floor - will vary depending on the bird species you want to attract. For example, the entrance shouldn't be any bigger than 2.5 cm in diameter if you want to attract wrens. Otherwise, sparrows or starlings may move in. On a larger scale, with a bigger entrance hole, the same basic design will attract nesting woodpeckers, screech-owls, and kestrels.
- After choosing the appropriate dimensions, cut one floor panel, one roof panel, two side panels, one back panel, and one front panel. Assemble the panels according to the diagram.
- Use screws instead of nails to make it easier to correct mistakes. Five cm coated flathead screws are best; they will allow you to open the hinged roof on one side of the box. That way, you can clean the box thoroughly every fall to get rid of parasites. Too many parasites can weaken and kill nestlings.
- Your box will last longer if the panels are held together with screws and bond-fast glue.
- Don't attach a platform or perch outside the box. Predators could raid the nest, and young birds might venture out of the box before they can fly.
- A nesting box made of dressed lumber must be treated with waterproof varnish to last many seasons. If you paint the box use subdued brown, tan, or grey, as birds are more likely to be attracted to these colours.
- To darken and preserve a new pine box, mix a little green or brown oil-based paint with linseed oil. Don't use lead-based alkyd paints or creosote wood preservatives, and don't treat the interior of the box with preservatives or paint.
- Drill a few small holes on the sides of the box (just below the roof overhang) to allow air and a little light to filter in. A few holes drilled in the floor near the walls will let moisture drain out.
- Cover the entrance until it's nesting time for the birds you hope to attract. Starlings and sparrows nest early and frequently take over boxes intended for other birds. They are also partly responsible for the decline of many cavity-nesting birds.
- Don't put nesting materials inside the box - birds would much rather find their own. You can, however, help out by making materials available outside. See "Provide Nesting Materials for Backyard Birds" for suggestions.
- The box will more likely be used if it's placed on a pole, mounted on a tree trunk, or suspended from a branch with a hook screwed into the roof.
- You can discourage unwanted visitors by putting a guard, such as a tin collar, around the trunk.
- Pick a spot that's sunny at least part of the day. Turn the entrance away from the usual direction of wind and rain - birds don't want a storm in their living room!
- If you want to relocate a nesting box, fall is a good time. You may want to add a few new boxes, or move old ones to better spots.
- Clean your nesting box each fall to get rid of parasites and leave a spotless house for next spring's family. It's a good idea to wear a face mask (available at hardware stores) to avoid breathing fungi and parasites. Scrub the box with a stiff brush and pour boiling water through it for disinfecting purposes. An alternative is to disinfect the box by spraying the inside with pyrethrum insecticide containing 0.5 percent pyrethrin. This insecticide was originally made from dried chrysanthemums, but is now artificially made. It is toxic to insects but will not harm birds. As well, its effects don't last long, which makes it safer for use in nature.
- For species like bluebirds, which sometimes nest twice in a summer, remember to clean house between broods. Removing the first nest will prevent adults from building another one on top of it. If this happens, the new nest could be raised dangerously close to the entrance hole, making chicks easier prey for starlings or raccoons.
- Nests left in boxes over the winter will probably attract mice, which love to stuff the cavities with grass and other vegetation. Birds are not likely to use such a box in spring.
- Check on a regular basis that the structure is in good repair.
- See that your box is mounted securely. Be sure the first heavy rain or windstorm won't blow it down. An accident could wreck the house and kill nestlings.
- If the roof is loose, the bottom warped, or a side cracked, take it down for repairs. If it needs painting or staining, do it in the fall. Return the box to its place outside so it can weather all winter. When spring arrives, the smell of the paint or stain will have worn off.