As bison migrate back into Yellowstone National Park, enormous, rock-hard snow berms are a deadly obstacle. Local volunteers are doing something about it.
Over five feet of snow fell on West Yellowstone through the winter, and more may come. Using their immense heads and horns, bison are experts at plowing through snow, but only in natural conditions. When snow plows clear roads, snow berms far larger than five feet are created on both sides, which then re-freeze and pack into insurmountable walls.
As bison attempt to cross roadways in their return migration, these tall berms can trap them – leaving each at the mercy of oncoming traffic. Last December, 13 bison died in a single incident when a semi truck plowed into such a scenario. Which is why the Buffalo Field Campaign (BFC) is stepping up.
At least 19 of Yellowstone’s most iconic species have been struck and killed on highways in the 2022-2023 winter, the organization says. So with help from Montana Department of Transportation (MDT), BFC volunteers have hand-dug tunnels for returning bison.
As local KBZK Bozeman reports, Highway 191 is an area of great concern. Thanks to BFC’s “dug-out corridors,” however, these giants can now travel quickly from one side of 191 to the other. The alternative is walking down the road for miles in search of a crossable spot – which is exactly what leads to collisions that are deadly for both bison and drivers.
According to the outlet and organizations, each tunnel is strategically placed along the historic, “preferred” routes of migrating Yellowstone bison. And so far, their hard work is doing the trick.
Ecosystem Engineers: The Ancient Migration of Yellowstone Bison
In winter, Yellowstone bison form herds of around 20 in size, down from an immense 200+ in the height of summer. These smaller herds move to lower elevations as dense snow accumulates in their summer ranges. And while immense snowpack forms on the areas they leave behind, herds wander their ancestral migration routes in search of grazing.
The most traveled species of the Greater Yellowstone Ecosystem, most bison will travel a good 1,000 miles every year. A chunk of this comes as they migrate between winter and summer ranges, which can be 70 miles apart. As they move with the seasons, these iconic ungulates may leave and return to the same areas repeatedly.
This behavior ends up shaping entire habitats. Known as ecosystem engineers, bison move outside the typical “green wave” of plants that sprout as spring returns. Instead of feasting on the wave as it moves through their range, they continually return to the same grazing areas. This recurring feeding sends plants into a sort of hyper-growth as they contend with the bisons’ feeding, which in turn creates bountiful and hardy ecosystems while leaving the green wave intact.
By comparison, other ungulates (hoofed mammals) follow and feast on the green wave specifically. If left unchecked, populations of deer, etc. would wipe out entire ecosystems by following and feasting on budding plants over vast distances. But not the bison.
For more on the beloved species, see our Yellowstone National Park Wildlife breakdown next.