Part of the BLM's mission is to help restore balance to wild horse herds which have no natural predators, accomplished largley through the wild horse and burro adoption program.
One of the BLM’s key responsibilities under the 1971 law is to determine the “appropriate management level” (AML) of wild horses and burros on the public rangelands. These animals have virtually no natural predators and their herd sizes can double about every four years. As a result, about 29,000 wild horses and burros roam BLM-managed lands in 10 Western states, a population that exceeds by about 1,500 the number that can exist in balance with other public rangeland resources and uses. 
To help restore the balance, the BLM gathers some wild horses and burros and offers them for adoption or sale to those individuals and groups willing and able to provide humane, long-term care.