As late winter turns toward spring, local birds will soon begin to look for mates and nest sites. Along with birds that make their nests on branches or in the crotch of a tree, there are many species that nest in cavities. But finding the right hole in a tree is not always easy. Competition for these cavities is keen. Many areas may just not have enough holes in suitable habitat. Smaller birds such as the Eastern Bluebird (Sialia sialis), Tree Swallow (Tachycineta bicolor), Black-capped Chickadee (Poecile atricapillus), Tufted Titmouse (Baeolophus bicolor), House Wren (Troglodytes aedon), and others often depend on woodpeckers to create holes for them.
You can help birds that nest in cavities by putting a nest box in your yard or a nearby preserve. Large yards, pastures, orchards, fields, cemeteries, and other empty spaces are all good places for a nest box for Eastern Bluebirds. Because bluebirds and most other birds feed almost exclusively on insects during the nesting season, it is important not to place a box where insecticides and herbicides are used. You may read that nest boxes should be up by the end of March, but you have some flexibility because many species have multiple broods.
In the past, bluebirds often nested in the holes of wooden fence posts in agricultural areas. Loss of rural farmland and orchard habitat and the replacement of wooden posts with plastic and metal have contributed to population losses. Another major factor in bluebird decline was the introduction of the non-native European Starling (Sturnus vulgaris) and House Sparrow (Passer domesticus). Both are very aggressive cavity nesters and will kill bluebirds. Starlings can be kept out of bluebird nest boxes that have the properly sized 1.5 inch (4 centimeter) diameter entrance hole. However, the smaller hole won’t deter House Sparrows from trying to use the box. You’ll need to be vigilant and pull out any nesting material from House Sparrows. House Sparrows also like perches, so the nest box should not have one. A large nearby tree will offer a place for the bluebird fledglings to fly to for safety. Keep the box in the open with the entrance pointed away from prevailing winds and at least 50 feet (15 meters) away from the woodland edge (to discourage House Wrens from using it).
If you would like to make your own box, here is a bluebird box plan from the North American Bluebird Society. You can also buy a nest box from your local bird store for the species you are interested in. A nest box should always be on a pole and not on a tree where predators can reach it. Boxes should also have a predator guard attached to the pole and below the box to keep out Raccoons (Procyon lotor) and Black Rat Snakes (Pantherophis alleghaniensis), which prey on bluebird adults and young.
Clean out the nest box after the birds have fledged. The adults will sometimes have another brood. It is also important to clean and disinfect the box with a weak bleach solution at the end of the nesting season, since bluebirds and other cavity-dwelling species will use the box during the winter as a place to roost and stay warm.
Beside its size, the location of a nest box will determine what species of bird you will attract. Black-capped Chickadees and Tufted Titmice prefer boxes placed in woodlands and forest edges, often under or near mature trees. House Wrens like to nest near brushy areas and in woodland edges. You’ll know you have a House Wren nest if you see the inside of the box filled with sticks. Here is a nest box plan from Cornell University that works for Black-capped Chickadees, Tufted Titmice, and House Wrens.
Black-capped Chickadees will nest in abandoned Downy Woodpecker (Dryobates pubescens) holes, but they will also excavate their own holes in rotten branches, often selecting birch (Betula sp.) or alder (Alnus sp.) trees. Chickadees like to have a 4 to 5 inch (10 to 13 centimeter) layer of wood shavings inside the box, so that they can excavate a nest cavity.
You can create woodpecker habitat by keeping a dead tree as a snag. In my yard, I had loggers leave a 20 foot (6 meter) tree stump from an American Ash (Fraxinus americana) that died. As the standing trunk decomposes it will provide an insect smorgasbord for a host of bird species as well as nesting sites.
Having a yard with mostly native plants will attract many insects that will feed birds and their young. Human activities hurt many bird species, but we can also do our part to support birds. Planting native herbaceous plants, trees and shrubs and putting up nest boxes are great ways to help.