After more than a century and a half of silence, massive American bison are once again crossing the dry grasslands near Cuatrociénegas, Coahuila. In the Chihuahuan Desert’s El Santuario reserve, a herd of about 47 animals has returned to land that last saw them in the 19th century. Social media quickly spread the claim that these bison “restored the ecosystem itself” in just months. The story is real. The punchline needs a closer look.
In August 2025, three bison arrived at the roughly 4,000-hectare El Santuario Wildlife Management Unit, a former cattle ranch inside the larger Cuatrociénegas protected area. That November, 44 more mostly females traveled from the established Rancho El Uno conservation herd in Chihuahua’s Janos Biosphere Reserve. Officials from SEMARNAT, CONANP, Fundación Pro Cuatrociénegas, the Mexican Fund for the Conservation of Nature, and Cuenca Los Ojos confirmed the transfers. The animals were locally extirpated, not extinct across Mexico. Hunting, habitat loss, and expanding ranches wiped them from this stretch of Coahuila roughly 160 to 200 years ago.
The bison are ecosystem engineers. Their hooves break up the compacted layer in the soil, letting rain seep down. Grazing prevents the buildup of dead grass, which reduces the risk of wildfires. Their feces fertilize the soil and attract dung beetles that aerate it. Seeds get tangled in their fur and are spread around by the animals.
“The bison could regenerate soils, improve water infiltration, reduce wildfires and increase biodiversity of the Chihuahuan Desert,”
Says project director Gerardo Ruiz Smith.
The signs of success became evident within several months the growth of new grass and better soil structure, as well as camera trap records of pumas, bobcats and collared peccaries. Local birds were seen using bison wool as nesting material. Calf births have already brought the herd size to around 50 individuals. These signs are consistent with expectations from a keystone species being introduced into a degraded grassland environment.
Through reintroduction, another herd is added to the increasing number of conservation herds in Mexico. The current project can be one of the methods that can help find out whether native large herbivores can rehabilitate the arid areas. Considering the process of grasslands rehabilitation in the U.S., this project may become a good case study.
