Introduction

Humans in eastern North America have been dependent on forests and their products for thousands of years. When the first Europeans arrived in North America, about 50% of the land or about 1.1 billion acres (445 million ha) were forested (Yahner 1995) (Figure 1). About three-fourths of this forested land occurred in the eastern half of the continent. Forests in the eastern United States remained relatively undisturbed until the late 18th century. Since then, the amount (area), age, size, shape, and structure of eastern forests have changed dramatically in response to logging and changing land use. By the 1850s, an estimated 120 million acres (48 million ha) of forest in the eastern United States had been converted to agriculture, and much of the remaining forest land had been logged at least once. Since the early 20th century, the natural reversion of farmland back to forest has increased the amount of forested land in the coterminous United States by over 20% (Yahner 1995). Furthermore, ecological succession, along with improved silvicultural practices, have converted many of the forests harvested in the 19th and early 20th centuries into sustainable, functioning forests.

Figure 1. Until the late 18th century, most of the 335 million acres of forested land in eastern North America existed as huge expanses of contiguous forest. Photo by Richard E. Bonney, Jr.

Today, the dynamic nature of eastern forests continues. Some contemporary forests are being lost and degraded primarily through residential, commercial, and industrial development, along with road construction. In addition, some types of timber-harvesting practices, such as clearcutting, can temporarily fragment otherwise contiguous, mature forests. The effects of this new wave of forest loss on birds and other wildlife are potentially greater than even the large-scale clearing of the past century, because in many regions forest loss owing to development is permanent. How have these historical and contemporary changes to eastern forests affected wildlife species, including forest-dependent songbirds?

At the extreme, the Ivory-billed Woodpecker, Carolina Parakeet, and Bachman's Warbler have become extinct, in part, because of deforestation (loss of forest habitat because of conversion to nonforest land uses). The fact remains, however, that most bird species in eastern forests are still abundant despite enormous alterations to their habitats. Several species, such as the Wood Thrush and Cerulean Warbler, are declining, but it's not too late to begin implementing habitat conservation plans for these species (Figure 2). If we wait until birds are in serious decline or endangered, our conservation efforts will be costly in terms of financial resources and pressures on society. Indeed, the primary objective of the bird-conservation initiative, Partners in Flight (see "What is Partners in Flight?" sidebar) is to keep species from ever reaching the threatened or endangered liststhat is, to "keep common birds common."

Figure 2. The Wood Thrush, which shares habitat requirements with the Scarlet Tanager, is a common but steadily declining species throughout much of its range in the United States. In its breeding range, the primary threats are habitat loss and lowered reproductive success as a result of habitat fragmentation. Photo by Mike Hopiak.

During the 1980s, biologists and birders began to notice long-term population declines among Neotropical migratory birdsspecies that breed in temperate regions of North America and migrate to Central and South America and to the Caribbean to spend the winter. Among the declining species were many birds of grassland and early successional habitats, as well as some birds that depend on mature forests. During the past 20 years, we have learned a great deal about the probable causes for the decline of these species. For example, we know that deforestation and unregulated pesticide use threatens birds in Central and South America and that collisions with radio towers and glass-covered skyscrapers kill thousands of migrating birds each year. We also know, however, that land-use and forest-management practices in temperate North America profoundly influence the breeding success of forest birds. For many of these species, our greatest opportunity to reverse population declines depends on the way we manage our forests on public and private lands.

Not all forests are equally valuable to birds, in terms of providing food, cover, or nest sites. Each bird species has a unique set of habitat requirements based on its ecology and behavior. Suites of species may respond similarly, however, to variation in such forest characteristics as tree-species composition (for example, northern hardwood or Appalachian oak), elevation, hydrology, forest age, patch size, shape, and surrounding land use. Obviously, some of these characteristics, such as forest type and elevation, are not easily manipulated. On the other hand, through careful management, many characteristics of forests can be manipulated to benefit birds.

This is the first publication in a forthcoming series of habitat management guidelines that will be produced by the Cornell Laboratory of Ornithology. This particular publication focuses specifically on mature forests in eastern North America, recognizing that regenerating forests and other early successional habitats also provide valuable habitat for many bird species. Our aim is to describe the kinds and amounts of forest habitat required to sustain healthy forest bird populations. This guide focuses on the Scarlet Tanager, a brilliant denizen of many mature eastern forests. Providing adequate habitat for this Neotropical migrant songbird will also benefit a wide variety of other forest birds. It's now time to begin applying what we've learned to reverse existing population declines and ensure that common species remain common.