Scrub/successional Bird Species

Summary of Geographic Patterns

Species Richness

The largest numbers of scrub/successional bird species are associated with the scrub deserts of the southwestern U.S., especially portions of Arizona and Texas. Species richness is also fairly high in east-central North America from Missouri, Tennessee, and the Carolinas north to the Great Lakes, and in portions of California. The fewest species occur in the Great Plains and Great Basin regions as well as the Florida peninsula.

Population Trends

Declining trends prevail throughout the eastern two- thirds of North America, and also from the central Rocky Mountains of Colorado and Wyoming across the Great Basin to California. Increasing trends are most evident in the southwestern deserts, and in the northern Rocky Mountains and adjacent Great Plains of Montana and Alberta.

Discussion

Scrub/successional birds have also shown a fairly consistent declining tendency throughout the history of the BBS, especially in eastern and central North America. Only 37% of the species have increasing trend estimates since 1966. Habitat loss, especially the natural succession of brushlands into forested habitats, is believed to be the primary factor responsible for these declining trends. The trends in this group are more positive in western North America, although local areas of decline are still evident in this region.