The committee was asked to

  • Evaluate BLM’s approach to establishing or adjusting AMLs as described in the Wild Horses and Burros Management Handbook (BLM, 2010).
  • Determine, on the basis of scientific and technical considerations, whether there are other approaches to establishing or adjusting AMLs that BLM should consider.
  • Suggest how BLM might improve its ability to validate AMLs.

To accomplish its assignment, the committee first investigated the basis of the Wild Horses and Burros Management Handbook approach to setting AMLs. The investigation included gaining an understanding of legislative definitions and interpretations that BLM has used to develop its AML policies. The committee then evaluated BLM’s approach to setting AMLs as described in the handbook. Finally, the committee explored alternative, improved approaches that BLM could consider in setting and validating AMLs.

Scientific methods can be used to assess the condition of rangeland and its ability to sustain foraging and browsing animals. However, decisions regarding what kinds of animals should occupy the land, how many species should be in an area, how the land should be used, and what the balance of different uses of the land should be are questions of policy, not science. The committee’s task in this chapter is to explore the science behind the establishment and adjustment of appropriate management levels.


The Wild Horses and Burros Management Handbook was written in response to a critique by the Government Accountability Office (GAO) stating that, as of 2008, BLM had not provided formal guidance to its field offices on how AMLs should be established and that there was a lack of consistency in setting AMLs in the agency (GAO, 2008). The following summarizes the legislative context for establishing and adjusting AMLs. It then draws conclusions about the challenges inherent in establishing and adjusting AMLs on the basis of the committee’s review of the legislation.

The Legislative Setting for Establishment of Appropriate Management Levels

The Public Rangelands Improvement Act of 1978 amended the 1971 act to state that information from rangeland inventory and monitoring, land-use planning, and court-ordered environmental impact statements should be used to determine whether horses are exceeding AMLs. The 1978 Code of Federal Regulations (CFR) asserted that BLM should ascertain the optimum number of free-ranging equids supported by an area and that enough forage should be allocated to horses and burros to maintain them at that number in healthy conditions while considering an area’s soil and watershed conditions, wildlife, environmental quality, and domestic livestock (43 CFR §4730.3 [1978]). The concept of defining AMLs by the optimum number of horses that maintains a thriving natural ecological balance and avoids deterioration of the range was reaffirmed in Dahl v. Clark, 600 F. Supp 585, 592 (1984) and by the Department of the Interior’s Interior Board of Land Appeals (IBLA) (Animal Protection Institute of America, 109 IBLA 112, 119 [1989]).

Under its enabling legislation, the 1976 Federal Land Policy and Management Act (P.L. 94-579), BLM is required to manage public lands under the principles of multiple use and sustained yield. The agency’s objectives are

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