Layers of charcoal residue buried beneath the northern Montana prairie show that pre-Columbian indigenous hunters on the Great Plains once burned patches of grassland to stimulate new growth. This created a tempting feast for bison herds, which the hunters then used to lure the bison in for the kill. And that, archaeologists say, means that even relatively small, mobile groups of hunter-gatherers can have a bigger environmental impact than they’ve been given credit for.
It’s not the fall, it’s the sudden stop at the end
For a group of hunters on foot, like the ancestors of today’s Blackfeet people, one of the most efficient ways to take down large prey like the American bison is to simply chase a group of them off a cliff and then harvest the remains below. Various hunter-gatherer societies around the world have used versions of this tactic over the last several thousand years, leaving piles of animal bones (many with evidence of butchering or cracking to get at marrow) at the bases of ancient bluffs. It takes planning and coordination among many hunters—and a decent amount of luck.
In the uplands of north-central Montana, on what is today the Blackfeet Reservation, pre-Columbian hunters built mile-long stretches of rock cairns called drivelines, which hunters used to help them funnel buffalo herds from fertile grazing patches called gathering basins, toward the edge of a steep bluff overlooking a tributary of the Two Medicine River. At two different driveline sites, archaeologists have radiocarbon dated bison bones to between 900 and 1650 CE, with the majority of kills happening in the final 250 years of that period. (The sites are on a tributary flowing into the Two Medicine River from the north and another on a different tributary flowing in from the south.)
And at the same time, evidence suggests that those same hunters were burning patches of the prairie to spur the growth of fresh, tasty new grass in the gathering basins to lure in herds of hungry bison. Southern Methodist University archaeologist Christopher Roos and his colleagues, in a project designed by John Murray of the Blackfeet Tribal Historic Preservation Office, studied layers of sediment exposed in the riverbed walls of two tributaries of the Two Medicine River.
Each tributary would have had one of the drivelines and gathering basins in its drainage area, so those layers of sediment record what was happening in the gathering basin and along the driveline. At each site, the team, which included members of the Blackfeet Tribe, found between five and eight layers of charcoal residue, a sure sign of nearby prairie fires. These were radiocarbon dated to between 1100 and 1650 CE—the heyday of the bison jumps.