Wyoming is home to a significant portion of the nation’s wild horse population, a living symbol of the American West’s historical landscape. These free-roaming herds, often referred to as mustangs, are descendants of horses brought to the continent centuries ago, including those of Spanish origin and later, escaped ranch stock. The state’s vast public lands provide a habitat for these animals, making their management a complex and continuous endeavor. Their presence on the range is closely monitored, reflecting a balance between preserving this iconic heritage and sustaining the delicate high-desert ecosystem they inhabit.
The Official Current Population Estimate
The most recent official estimate of wild horses living on the range in Wyoming places the population at approximately 8,488 animals. This figure is derived from the latest data released by the federal agency responsible for their management, based on on-the-ground surveys and aerial counts. This number represents an estimate at a specific point in time, such as the March 1 count used for annual assessments. The actual number of horses fluctuates constantly throughout the year due to natural factors like spring foaling and management actions such as roundups and removals. Consequently, the population is a dynamic figure, making any single count an approximate snapshot.
Geographic Location and Federal Oversight
Wyoming’s wild horses roam across nearly five million acres of public land specifically designated for their use. These areas are officially known as Herd Management Areas (HMAs), and the state contains 16 of these distinct geographic regions. Major HMAs include the McCullough Peaks in the northwest, the White Mountain area overlooking Rock Springs, and the complex of areas around North Lander. These HMAs are spread primarily across the western and central portions of the state.
The management of these herds falls under the jurisdiction of a federal agency that oversees public lands. This authority is rooted in the Wild Free-Roaming Horses and Burros Act of 1971. This landmark legislation mandated their protection and management on federal lands, declaring them “living symbols of the historic and pioneer spirit of the West.” The law requires the agency to maintain a thriving natural ecological balance on the range.
Defining Appropriate Management Levels
The core concept guiding wild horse management is the Appropriate Management Level (AML). The AML is defined as the population range of horses that can be sustained by the range while ensuring a thriving ecological balance with other wildlife, vegetation, and water resources. Determining the AML involves complex ecological assessments that consider the available forage, water sources, and the needs of native species. The goal is to prevent overgrazing and land degradation that could harm the long-term health of the ecosystem.
For all of Wyoming’s Herd Management Areas combined, the established AML is set at a maximum of approximately 3,725 animals. This number is the highest population the range is deemed capable of sustainably supporting. Comparing the current estimated population of over 8,400 horses to this maximum AML reveals a significant disparity. The current number is more than double the level considered ecologically sustainable, which drives the agency’s management actions.
Strategies for Herd Population Control
To address the large number of horses exceeding the AML, the agency employs various population control methods. The primary strategy is the use of “gathers,” which are roundups designed to remove excess horses from the range. These gathers are conducted using techniques like employing helicopters to herd the animals into temporary corrals. A less intrusive method involves bait-trapping, where horses are lured into corrals with food and water. Once gathered, the horses are transported to off-range facilities for adoption or sale. The removal provides immediate, temporary relief, but it does not stop the natural reproductive rate, which can increase the population by up to 20 percent annually.
A longer-term strategy involves the use of fertility control vaccines, such as Porcine Zona Pellucida (PZP). This immunocontraceptive vaccine is administered to mares, usually by remote darting, to prevent pregnancy for one to two years. The repeated use of PZP has been shown to reduce the annual population growth rate significantly. While gathers offer immediate population reduction, fertility control aims to achieve a sustainable growth rate over time, helping to keep the population within the defined AML range.