Bison in the National Bison Range, Montana, 2003. Credit: Ryan Hagerty, Public domain, via Wikimedia Commons.

New research suggests prehistoric bison hunters abandoned a long-used site 1,100 years ago to adapt to a changing climate.

As drought and rising organisational demands for larger hunting operations hit at the same time, ancient hunters adapted to severe droughts by shifting the way and where they hunted, study shows

On the Great Plains of North America, bison were hunted for thousands of years before populations collapsed to near extinction due to overexploitation in the late 1800s.

But long before then, bison hunters used various strategies and different types of sites, sometimes switching between sites.

Now, researchers sought to understand why hunting stopped when bison continued to be present at the Bergstrom site in central Montana, where bison were hunted intermittently for around 700 years before the site fell into disuse.

First author Dr John Wendt, a paleoecologist and assistant professor of rangeland ecosystem management at New Mexico State University, said: “We found that bison hunters ceased using a kill site in central Montana around 1,100 years ago.

“It appears that hunters stopped using it because severe, recurring droughts reduced the water available for processing animals at a small nearby creek.

Site abandonment was a response to environmental stressors and changing social and economic pressures.”

Bison bones are scattered across the site. Credit: John Wendt.

More than bison

To understand what shaped choice of hunting sites and organisation, the team combined archaeological excavation, sediment coring, and laboratory analyses.

Wendt said: “The Bergstrom site presented a puzzle because it was used intermittently and abandoned when bison were common throughout the region and hunting was intense.

“Why would hunters stop using a site that had worked for so long?”

To get to the mystery’s core, the researchers dug nine 1×1m excavation pits in the spring of 2019.

Excavated materials were documented and photographed and charcoal fragments were sent off for radiocarbon analysis.

Two sediment cores were collected directly next to the excavation area. The team analysed these for pollen and charcoal fragments.

They also tracked the presence of large herbivores and analysed climate reconstructions.

Based on this, the team was able to see if ecological changes explained why Bergstrom was abandoned, or if something else had driven hunters away.

Wendt stated: “Abandonment wasn’t because the site became ecologically unsuitable in any absolute sense. Bison were still around, vegetation hadn’t changed, and there was no substantive shift in fire activities.

“Bison hunting activity was not simply following prey populations.”

Students conducting archaeological excavations. Credit: Michael Neeley.

Levelling up hunting sites

Instead, severe droughts stretching decades hit the region before and after final abandonment of the site.

Such droughts limited how much water was available, but also made locations where water wasn’t a given less attractive to hunter groups.

At the same time, many hunters reorganised themselves from small mobile groups working opportunistically to more coordinated, larger groups who used constructed infrastructure and occupied sites for longer time periods.

Wendt said: “These larger operations were based on large kills and could produce surplus for trade and winter storage, but they also meant more dependence on specific resources like water, forage for larger herds, and fuel for processing fires.”

Sites meeting these characteristics were more scarce, as they also needed topographic features suited to large bison drives, such as cliffs for jumps and features to contain herds.

If these characteristics were given, however, such sites often saw repeated, large-scale use over centuries.

Sophisticated climate adaptation

Favouring larger sites, however, meant greater dependency on everything going right, as these sites were harder to replace.

Hunters worked at these sites over generations and could reorganise as conditions changed.

Maintaining cultural knowledge and flexibility is most likely what allowed this type of hunting organisation to persist through climate variability, the team said.

This flexibility is also relevant to modern bison management systems, which can increase their odds of persisting through climate variability by retaining the capacity to reorganise how and where animals are managed.

The team pointed out that their conclusions may not hold true for other bison hunting sites in the region, which may have been abandoned for other reasons.

In addition, while the study shows use for around 700 years, it could not determine how long each use period lasted or how frequently the site was used during this time.

It is also possible that after abandonment, the Bergstrom site saw infrequent, low-impact use that left minimal traces that could not be detected, the team said.

Wendt concluded: “While people have been adapting to the climate for much longer, Bergstrom’s abandonment shows that people reorganised in response to recurring droughts in the last 2,000 years.”

The results were published in Frontiers in Conservation Science.