Words On Birds by Steve Grinley
Bird Houses Help Cavity Nesting Birds
March 25, 2022
by Steve Grinley
Many North American birds are cavity nesters – that is, they nest in holes in trees and fence posts. Woodpeckers can use their strong bills to chisel holes to create their own cavities. Most other birds, such as chickadees, house wrens and titmice must find abandoned cavities in which to nest.
Not unlike the current lack of inventory in our own real estate market, the birds also have a hard time finding adequate natural cavities. Man is too quick to clear timber, especially dead trees, to give woodlots and yard edges a more “pristine look.” As trees are cleared, so are the potential cavities for birds.
An even greater threat to our cavity nesting native birds has been house sparrows and European starlings, birds introduced from Europe, which are also cavity nesters. These aggressive birds have displaced many of our native birds from the tree cavities that exist.
One way to help solve the housing shortage for our birds is to provide artificial cavities known as birdhouses or nest boxes. More than fifty species of birds – including bluebirds, tree swallows, great crested flycatchers, kestrels, chickadees, nuthatches, wrens, kestrels, owls, wood duck and woodpeckers – will use nest boxes. A birdhouse on your property may provide a nest for birds and some enjoyable bird watching for you.
March is a good time to inspect, clean and repair any existing birdhouses that you have. Clean out any old nesting material and brush out the inside walls with a wire brush. You may also wash out the box with a mild detergent solution, rinse thoroughly, and let it dry completely. If squirrels have enlarged the entrance hole, you can add a new wood predator guard over the hole to reduce the hole size again. Metal guards can be placed over holes to prevent future chewing. Metal guards may be a good idea on any new houses you put up if squirrels are a potential problem.
Migrating robins have started to arrive. Phoebes will also starting to arrive and barn swallows will return in April. These three birds have adapted to man by often nesting on ledges of man-made structures. They won’t use a typical birdhouse, but they may use an open nesting shelf placed on a house, deck, garage or barn.
Where you live and the type of habitat that you have in your yard will be determining factors in which birds you may be able to attract. Bluebirds, tree swallows and purple martins prefer open areas, house wrens like brushy edge areas, while chickadees, nuthatches and titmice prefer more wooded areas.
To attract the bird you want, it’s best to start with a birdhouse that is built to specification for that bird and place it in a suitable area. The entrance hole size is one critical dimension. House wrens, for instance, can squeeze into a 1-inch opening that will eliminate larger birds. Chickadees, titmice, nuthatches and downy woodpeckers will use a 1 1/8 inch or 1 1/4 inch opening while bluebirds, tree swallows and house sparrows need a 1 1/2-inch opening. For most backyard birds, the house can be placed 5-10 feet off the ground. Face the houses away from northerly directions, as cold wind and rain can be detrimental in early spring.
Purple martins arrive in late April and May. They nest in colonies and need an open area, preferably with water nearby. Their apartment houses should be erected high, 12-15 feet or more. The house needs to be accessible though, to enable you to discourage house sparrows or starlings from nesting in the house before the martins arrive. Attracting purple martins requires more work initially than attracting some other birds, but once martins establish their colony, they will return faithfully each year. In fact, many birds such as bluebirds, tree swallows and nuthatches, return to the same nest site each year.
Also please remember that not all birds will nest in a house. Only those birds that naturally nest in tree cavities will use a nesting box. Every year we are asked for houses for cardinals or goldfinches. These, like so many birds, build their nests on limbs of trees or in dense shrubs and will not nest in a birdhouse.
Encouraging birds to nest in your yard by providing nesting boxes is beneficial to you as well as the birds. Birds can help control the insect populations on your lawn, in your garden and on your shrubs without the use of harmful chemicals. Many birds eat flying insects, while many other species such as wrens, bluebirds and woodpeckers eat crawling insects. This natural insect control will be a benefit all summer long.5