Birds are essential components of forest ecosystems. Small fruit-eating and insectivorous birds disseminate seeds and help regulate insect populations. Large predatory birds control small-mammal populations, and birds serve as food for other species, including humans. Some birds, such as woodpeckers, construct nest cavities that later serve as shelter for other animals. Scavenging birds help decompose animal and plant material on the forest floor. And, the beauty of bird song and flight provides incomparable aesthetic value.
Forest attributes of composition and structure are important to forest bird species to varying degrees and during different seasons. These attributes include: species of trees and understory vegetation, tree diameter, canopy and understory height and density, and abundance of standing dead trees and downed dead wood. The arrangement of forest and non-forest habitat on the landscape also plays an integral role in the ability of forests to meet bird life cycle needs.
All types of forests are important for birds, and each bird species is adapted to the forest in which it resides. Suitable bird habitat provides food, water, shelter, nest sites, song posts, and perching sites. Some species, such as mockingbirds and crows, are habitat generalists: they occupy a wide range of habitats and are not dependent on any one type. Others, such as the red-cockaded woodpecker and Kirtland’s warbler, are habitat specialists and require a specific habitat type or feature for all or a critical part of their life cycle. The red-cockaded woodpecker, for example, makes its nest only in living pine trees.
Forest breeding bird species diversity in the United States generally increases from southwest to northeast following gradients of moisture, topography, and vegetation. US oak-pine and oak-hickory forest types support around 150 to 200 species of breeding birds, while coniferous forests support about 150 species. Bird species diversity increases with forest succession in deciduous forests. Up to 75 percent of bird species in deciduous forests are neotropical migratory songbirds, which actually spend most of each year in other habitats, from the southern United States to Central or South America.
In general, diverse landscapes support more species than do uniform ones with little variation in topography or vegetation. For example, mountainous regions tend to support numerous avian species because of the habitat diversity associated with topographical changes. Forest management techniques such as thinning or prescribed burning are sometimes used to manipulate forest communities to target a specific species or to support overall avian diversity in a stand or on the landscape.
The flammulated owl (Otus flammeolus) is an example of a species that has specific habitat requirements for breeding. Like many owl species, the flammulated owl nests in cavities of live trees or in large standing dead trees, or snags.
Throughout most of their breeding range of western North America, flammulated owls inhabit mid-elevation montane forests of ponderosa pine (Pinus ponderosa) and Jeffrey pine (Pinus jeffreyi). This map shows the extent of those pine species and associated flammulated owl range. Potential flammulated owl breeding habitat is present on about half of this forest acreage, where there are trees of a large size and open cover.