Biological Inventories to identify bird species in six National Capital Region Network parks (Antietam National Battlefield, Catoctin Mountain Park, Harpers Ferry National Historical Park, Manassas National Battlefield, Prince William Forest Park, and Wolf Trap National Park for the Performing Arts) were initiated in 2001. The goals of the inventories were to identify 90% of the bird species occurring in each park and to determine their breeding status and spatial distribution. Surveys were concluded in 2003, and a total of 175 species were identified in the Network parks; species richness ranged from 76 species at Wolf Trap National Park for the Performing Arts to 151 species at Manassas National Battlefield. Two methods were used to assess the completeness of the inventories (i.e., 90% species documentation): a direct comparison to an expected species list and species accumulation curves. Based on the results of the two methods of analysis it was concluded that 90% of the species had been documented in the six network parks. Additional inventories, utilizing a different survey methodology, may be beneficial to document the occurrence of the remaining species.