Written by: Ron Rohrbaugh, Director of Conservation Science and Forest Programs for Audubon Pennsylvania
Birds are integral parts of forest ecosystems. Worldwide, insectivorous birds consume 400-500 million tons of insects each year, while other species cache seeds that promote tree regeneration and pollinate flowering plants. In so doing, forest dwelling birds provide ecosystem services that support overall forest health. There are hundreds of papers in the scientific literature that illustrate the importance of birds in maintaining both ecological and socioeconomic systems. It’s safe to say that without robust bird populations, forests could not exist in a healthy state. It’s also safe to say that stable, resilient bird populations cannot persist without adequate amounts of healthy forest to support all phases of their lifecycles.
The importance of private lands to global forest-bird populations cannot be overstated. This is especially true in eastern forests where more than 80% of forest birds rely on privately owned forestlands for nesting and brood rearing. Any loss of this forest habitat, stemming either from deforestation or degradation, results in lowered carrying capacity for these already declining species. A recent paper in the Journal Science (Rosenberg et al., 2019) revealed a 50-year loss of 170 million eastern forest birds, representing 17% of the population.
Each species of forest-dwelling bird has its own specific habitat requirements that can be approached on an individual species basis or by suites of species that have similar needs. Some birds prefer to nest in mature forests with a relatively closed canopy, while others prefer to nest in young forest habitat that has shrubs and sapling-sized trees with high stem density, thick foliage, and few overstory trees. In addition, there are forest birds that will use both mature and young forest habitats for nesting (Hartley et al. 2004).
A shifting mosaic of forest age classes and forest types in the landscape provides nesting habitat for birds with different needs. This mosaic also provides a diverse array of habitats where birds can raise their young after they fledge from the nest. Birds that nest in mature forest will frequently move their fledged young to areas with a dense forest understory or to young forest habitat, where they can seek cover and forage in dense foliage and stems. The converse is also true, as birds such as the Golden-winged Warbler nest in young forest, but move their family groups to older forest to forage and prepare for fall migration.
Forested landscapes that are composed of approximately 10-20% young forest (typically less than 10 years of age) and the remainder in intermediate and mature forest, provide an optimal mix of habitat for a suite of forest birds. In other words, the interspersion of forest age classes and types provides the greatest opportunity for a healthy, diverse community of breeding forest birds.
What does this need for landscape-scale interspersion mean for management strategies? Landscapes with at least 70% forest that are managed on a roughly 100 year even-aged rotation with 10-20% young forest always being present will usually provide the greatest potential to support a healthy suite of forest birds. In landscapes where forest cover is less than 70%, land-use decisions should discourage converting existing forests to other cover types and encourage reforestation of non-forest sites. Within fragmented landscapes, forest management can improve habitat for birds by considering forest patch size and potential edge effects, as well as focusing on improving within-stand structure.
The largest opportunity for recovering bird populations and stabilizing declining forest health without investing massive resources is to capitalize on routine, private forest management. This is especially true on land trust properties where sustainability and wildlife-habitat enhancement are often primary goals. To learn more about managing for Eastern-forest birds, please read these new publications from Audubon Mid-Atlantic. Healthy Forests: A Bird-based Silvicultural Guide for Forestry Professionals and the Forest Bird Pocket Guide.