Bird house plans can vary according to which species you wish to attract to nest in your backyard. There are nest box plans specific for bluebirds, wrens, chickadees and purple martins. Each bird house design consists of a roof, sides and bottom, but there can be different dimensions for each species.
For wrens you can use either a 4-inch by 4 or 6-inch floor with 8 inch walls. The hole should be centered six inches above the floor with a diameter of 1 1/8". For bluebirds, use a 5 1/2" x 5 1/2" floor, ten inch walls with a 1 1/2" centered hole six inches above the floor. If you make your holes larger, house sparrows and starlings will be able to enter the house and take over the bird house and sometimes even kill the adults and/or nestlings.
Bird house plans should not include placing a perch on the nest box. This will invite potential predators, such as aforementioned house sparrows and starlings as well as raccoons, cats and snakes, and enable them to easily find a way into the house. To further discourage uninvited predators if your bird house is mounted on a pole, place a predator guard or baffle below to keep pests from climbing up from below.
Make sure you have holes to allow for drainage and ventilation. This can be done by cutting a small cut off each of the corners of the floor. The roof should always be attached at an angle, slanted so that rain can drain off and not collect. Wood should be at least two inches thick to provide for insulation against the heat and cold. The wood should not be treated and only painted, although usually not necessary, with non-toxic paint.
Of course if you are building any kind of bird house with a entrance hole, you will be attracting those species who are cavity nesters. If you want to have robins or phoebes nesting in your backyard, you will have to build a nest shelf or platform, because they often will like to nest on ledges. Build a 6" x 6" x 8" sided shelf with the front open. Place under the eave of the house, under the deck or in a barn to attract barn swallows.
Purple Martin bird house plans are made not for just one pair of birds, but rather for many. Purple Martins like to nest in colonies so you will be building a condo-like house with several units, depending upon how many you wish to have nesting in your backyard. Each unit should be 6" x 6" x 6", have a 2-1/2" hole placed 2-1/4" above the floor.
When choosing a bird house plan, just keep in mind that you are building a house for the birds to have a sheltered, safe place to raise and ultimately fledge their young. Fancy designs with all kinds of unnecessary adornments are not going to appeal to potential tenants. The right dimensions will provide the right feel and attract the right birds.
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