Following passage of the Wild Free-Roaming Horses and Burros Act in 1971, limits for the number of horses on each herd unit (referred to as Herd Management Areas or HMA's) were set. These limits or population goals are referred to as Appropriate Management Levels or AMLs. From 1980 and through the present, more active management reduced wild horse numbers closer to AMLs. Wild horse numbers were reduced to about 40,000 by 1999 and to about 37,186 wild horses in 2003, prior to the foaling season. Some 203 HMAs are managed by the BLM across the Western U.S. The responsibility of monitoring range conditions; allocating range resources between horses, livestock, and wildlife; monitoring horse and burro numbers and managing their population levels represents a large federal management responsibility. The number of animals in most herds are counted or estimated every three to four years, in order to plan for any gathers, and adoptions. Herd management activities, such as gathers and removals, take place for most herd areas every four years.