The American Bison, or Plains Bison, is a powerful symbol of North American wilderness, representing the vast, open grasslands that once defined the continent. While their presence was long restricted to the plains of the United States and Canada, bison have successfully returned to Mexico. This reintroduction is a carefully planned conservation success, representing a victory for ecological restoration. The effort aims to restore the natural ecological balance of Mexico’s northern desert grasslands.
The Historical Range and Extirpation of the Plains Bison
The historical distribution of the Plains Bison extended into the northern territories of Mexico, marking the southernmost limit of their continental range. Archaeological records confirm the bison’s presence in the states of Sonora, Chihuahua, Coahuila, Nuevo León, and Durango, with evidence dating back to at least 700 CE. These animals were an integral part of the Chihuahuan Desert grasslands ecosystem for centuries.
The bison population faced extirpation in the latter half of the 19th century due to intensive human activities. Excessive hunting pressures, fueled by commercial demand and government-backed culls in the U.S., decimated the northern herds. This hunting, combined with the expansion of agricultural and livestock operations, led to habitat loss and fragmentation. By the early 20th century, the Plains Bison was considered locally extinct in Mexico.
The Conservation Strategy for Reintroduction
The effort to return bison to Mexico began with securing genetically pure individuals. The first major reintroduction phase was launched in 2009 at the Janos Biosphere Reserve in Chihuahua, a protected area of Chihuahuan grassland.
The source herd was selected from Wind Cave National Park in South Dakota, United States. A group of 23 specimens was transferred to the Janos reserve, managed by the Mexican Fund for the Conservation of Nature (FMCN). The primary goal was to establish a herd free of domestic cattle genes, ensuring the long-term genetic integrity of the new population.
The success of the Janos herd led to the development of a second conservation herd to increase the species’ security and distribution. In 2020, 19 bison from the established Janos population were translocated to the El Carmen Nature Reserve in Coahuila. This strategic expansion involved collaboration between government agencies and private companies to re-establish the bison across its former range.
Monitoring the Current Mexican Bison Population
The Mexican bison population reflects successful conservation, with herds showing strong growth rates. The initial herd at the Janos Biosphere Reserve in Chihuahua has increased since its reintroduction. By May 2017, the Janos herd reached 138 individuals, serving as a source population for other reintroduction sites.
The second herd, established in 2020 at the El Carmen Nature Reserve in Coahuila, also expanded quickly. Starting with 19 specimens, the population reached nearly 100 individuals by 2023. Distribution efforts continued with a relocation of 44 bison from the Janos herd to the Don Martín National protected area in Coahuila, establishing a third conservation nucleus.
Monitoring is achieved through a comprehensive population management strategy that balances expansion with ecological sustainability. This involves herding, recording, and selection of individuals to maintain a healthy herd structure. Management teams regulate population growth to prevent overgrazing and address potential health concerns, such as disease management.
The Role of Bison in Restoring Grassland Ecosystems
The return of the Plains Bison to northern Mexico is significant for the entire grassland ecosystem. Bison are considered keystone species and “ecosystem engineers” because their behavior maintains the health and biodiversity of the Chihuahuan Desert grasslands.
As they graze, bison prune grasses evenly, promoting the growth and diversity of other plant species. Their digestive process aids in seed dispersal, carrying seeds and depositing them with natural fertilizer, which helps vegetation regenerate. Physical actions, such as wallowing and trampling, create microhabitats that benefit smaller creatures.
Flattening vegetation in patches is particularly beneficial to species like the Mexican prairie dog, providing better sightlines to watch for predators. The grasslands maintained by bison also play a role in climate resilience, acting as a carbon sink. These restored prairies absorb carbon, making the bison’s presence an important component of the region’s defense against climate change.