Photo: Pexels/Juraj Valkovic

Once upon a time bison roamed in large herds across Europe, but a century ago they went extinct on the continent with just three dozen of them languishing in captivity.

Conservation efforts have been successful in reintroducing bison into Europe and the animals’ numbers are on the rise. But to ensure their long-term survival this time around, we have to understand why they nearly went extinct in the first place. This is what a team of scientists has set out to do while also suggesting areas where rewilding attempts are most likely to succeed.

To do this, the scientists created a detailed simulation that “combined paleoclimate data, vegetation and habitat information, the population growth and expansion of Palaeolithic humans across Eurasia, and bison population and dispersal dynamics,” they explain in a study. “Historical records, fossil evidence, and ancient DNA were used to independently test the model’s accuracy.”

They then ran 55,000 different simulations to explore how climate, hunting, and changes in land use affected bison populations across Europe. “Toggling off different variables one at a time allowed [us] to test the importance of each variable,” they write. “If human removal of forests was turned down to zero, for example, and there was no change in bison abundance and range, then [we] would conclude that land use change likely was not a factor in the species’ demise.”

This allowed the scientists to reconstruct 21,000 years of European bison range dynamics. They found that the bison’s range began collapsing around 14,700 years ago owing to the rapid warming of the climate and its effects on bison habitats. At the same time, as human populations were growing, the bison were unable to bounce back through continued habitat loss and hunting.

“Hunting caused range loss in the north and east of its distribution, while land use change was responsible for losses in the west and south. The arrival of firearms in the 1500s dramatically hastened the species’s decline,” the scientists explain.

The threats of climate change, reduced habitats and poaching remain as strong as ever even today, according to Rafał Kowalczyk, head of the Mammal Research Institute at the Polish Academy of Sciences Kowalczyk who was a key member of the research team.

“The stories of the past are being repeated in the present,” Kowalczyk stresses. “Learning from the past, and understanding the process of species extinction, can help us better protect the species.”

Today, after decades of stepped-up conservation efforts, around 7,300 free-ranging European bison live around Europe, serving an important ecological role, but their populations are facing threats.

“[R]ewilding has been done without a strong understanding of habitats and regions where bison once thrived,” the scientists note. “As a result, the species has been released at sites ranging from the coastal dunes of the Netherlands to the mountains of the French Alps and the Mediterranean climate of Spain, with mixed success. Of the 47 free-living European bison populations, only eight have more than 150 adults, and all eight depend on supplemental feeding due to poor habitat suitability.”

The scientists say their model suggests that the regions most suitable for the species’s reintroduction include parts of Poland, Ukraine, and western Russia. “With habitat restoration, parts of the Balkans and Germany also have the potential to be good sites for bison reintroduction,” they argue.

“I hope that the maps we’ve produced can help inform future efforts in terms of where reintroduction efforts should occur,” says July Pilowsky, a disease ecologist at Cary Institute of Ecosystem Studies.

“It’s especially crucial because of the war in Ukraine. Over 50 percent of all free-living bison are in Ukraine, and conservationists are really worried,” Pilowsky adds.

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