The natural vegetation in which wild birds can hide from predators, build nests and raise young, glean food, and find protection from the elements is called cover. It is, perhaps, the most important ingredient for a successful backyard bird habitat. Without cover, the backyard is a biological desert that will attract little or no bird life.
A model backyard bird habitat has a bountiful selection of plant life, starting from the lowest forms, ground cover, planted closest to the house, and then graduating to small shrubs, larger shrubs, small trees, and finally large trees, as the distance from the house increases. This so-called stadium effect provides a variety of natural life zones, thus increasing the kinds of birds that will visit the habitat. If all the habitat niches are provided, then the birds in your region that require those natural niches are likely to feel comfortable in your habitat.
In other words, ground inhabiting birds like towhees, sparrows, and juncos will feel comfortable in the ground cover and small shrubbery nearest your house or patio. Buntings, finches, chickadees and mockingbirds will find the larger shrubs and small trees to their liking, slightly farther away from the windows. And in the mature larger trees with large canopies, such birds as tanagers, grosbeaks, orioles nuthatches and woodpeckers will find food and cover that suits them at the extremities of your backyard bird habitat.
Each region of the country has its own native and natural plant life that is suited to the birds of that region. When planning a backyard bird habitat, it is best to consult a nursery about the kinds of native plants, shrubs and trees that are best for the climate in your yard.
Houses: Houses for birds are also considered cover, as they are substitutes for natural cavities in trees and rocks. Houses range in size from very large to accommodate wood ducks, screech owls and kestrels, to very small for house wrens and chickadees. Bluebirds require slightly larger houses than wrens, and purple martins prefer apartment type house containing many units.
Backyards that offer nesting places in natural cover for birds that do not use birdhouses give the homeowners exceptional opportunities to see how birds build nests, lay eggs and raise their young at close range.