Habitat requirements of early successional bird communities: Management implications for mid-Atlantic region
Recent concern for the status of North American bird populations has resulted in an escalation of monitoring and management efforts. Although much of this concern has been focused on declining forest-dwelling species, species associated with grass or shrublands have experienced annual population declines that in many cases are equal to or greater than their forest-dwelling counterparts. Declines of many grassland bird species are evident from several geographic areas including the mid-Atlantic region. Although many factors may be involved, the widespread loss and degradation of early successional habitats represents the most plausible explanation for recent declines. If the pattern of land conversion observed over the past 40 years continues into the future at a similar pace, few grasslands will be available to support populations of declining birds. Because of the high concentration of military installations within the mid-Atlantic region, U.S. Department of Defense (DoD) lands may represent the most promising opportunity to sustain early-successional communities. DoD lands are particularly widespread and currently contain some of the most extensive grasslands in the region. Through its partnership with the Partners in Flight initiative, DoD has committed to integrate neotropical migratory bird management efforts into existing natural resource management programs that are consistent with the military mission. This project was initiated to determine habitat requirements for species within the mid-Atlantic region that depend on early successional habitats so that appropriate management recommendations could be formulated. Both breeding and winter bird communities were sampled within a network of study sites located on the coastal plains of Maryland and Virginia to determine the habitat and area requirements of birds that depend on early successional habitats. A total of 1, 182 individuals of 39 species were detected during the breeding season and 1,403 individuals of 46 species were detected during the winter. During both seasons, habitat type and patch size were important determinants of community organization. The results of this study provide regionalized insights into the habitat requirements of grassland and shrubland birds that are important to the development of appropriate management guidelines. The two most significant findings in this regard are that 1) patch area is an important habitat requirement for obligate grassland birds but not for shrubland birds, and 2) patch occupation by shrubland species is conditional on the availability of woody vegetation while occupation by grassland species is conditional on the absence of woody vegetation. Another important consideration in developing management recommendations is that within the mid-Atlantic region, large and small patches of early successional habitat are not equally abundant. Large patches are relatively rare within the landscape. Because obligate grassland species require large fields and large fields are regionally rare, we recommend that whenever possible fields greater than 10 ha should be managed for grassland species. Specific Management Recommendations include: 1. Consider patch size in developing site-specific management plans. 2. Manage grassland patches to prevent encroachment by woody vegetation. 3. Manage shrub land patches to maintain a stable area of woody vegetation. 4. Manage both grassland and shrubland patches to maintain or promote vegetation diversity. 5. Conduct management activities just prior to the growing season for both grassland and shrubland patches.