And winterkilled bison carcasses are a vital food source for grizzlies when they emerge from their hibernation dens in the spring.<\/p>\n
Even so, bison are better than most other critters at surviving whatever Wyoming winters can throw at them.<\/p>\n
A photo that the National Park Service recently posted on social media of a snow-and-frost-caked bison in Yellowstone garnered some sympathy from some viewers for the supposedly miserable creature.<\/p>\n
But make no mistake, the bison was completely in its element.<\/p>\n
![\"Wyoming\u2019s](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2025\/12\/Bison-and-snow-National-Park-Service-12.13.25.jpg\")
Wyoming\u2019s Yellowstone bison look miserable when caked in snow and frost, but their thick coats, fat reserves and efficient digestion keep them warm and fueled through brutal winters. Even so, late winter stress, thin ice and humans kill many each year. (National Park Service)Snow Is Insulation<\/p>\n
Being covered in snow might sound miserable from a human perspective. From a bison\u2019s perspective, it\u2019s just the ticket.<\/p>\n
\u201cAll that snow on the back means that the heat is staying inside the bison,\u201d National Bison Association president Ken Klemm told Cowboy State Daily.<\/p>\n
Bison’s internal fat layers, hide and hair all help trap their body heat, he said.<\/p>\n
The hide is \u201cspongy, which helps retain heat,\u201d he said.<\/p>\n
And the snow itself can act as an extra insulating layer for bison and other animals, biologist George\u00a0Wuerthner\u00a0told Cowboy State Daily.<\/p>\n
\u201cThat\u2019s what weasels do. They go under the snow\u201d because it can help retain their body heat, said Wuerthner, who has worked in the Greater Yellowstone Ecosystem for decades and is president of the Montana Wild Bison Coalition.<\/p>\n
While snow might stick to bison, they don\u2019t need to burrow under it to stay warm, because their bodies\u2019 \u201cvolume to surface area\u201d ratio helps them retain heat, he said.<\/p>\n
Whereas weasels are \u201clong and thin,\u201d so they\u00a0lose\u00a0heat quickly, Wuerthner said.<\/p>\n
Perfect Hair And An Internal Heater<\/p>\n
The winter fur that bison\u00a0grow can\u00a0keep them comfortable in nasty conditions.<\/p>\n
Studies from Canada indicate that it must plunge to about 40 degrees below zero \u201cbefore their metabolism even starts to adjust,\u201d Klemm said.<\/p>\n
A bison\u2019s winter hair acts \u201calmost like a down coat,\u201d insofar as it can trap pockets of warm air, and keep the animal toasty, Wuerthner said.<\/p>\n
Their winter coats are layered, with \u201cguard hairs\u201d that are long, and then a \u201cdowny layer underneath it,\u201d Klemm said.<\/p>\n
Bison generate their own internal heat, Wuerthner said.<\/p>\n
They have a four-part stomach system, and can get by on sparse, dry winter grass much better than domestic cattle could, he said.<\/p>\n
\u201cThat complex digestive system produces internal heat through the fermentation process,\u201d he said.<\/p>\n
![\"Wyoming\u2019s](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2025\/12\/Bison-and-snow-GettyImages-1136621097-12.13.25.jpg\")
Wyoming\u2019s Yellowstone bison look miserable when caked in snow and frost, but their thick coats, fat reserves and efficient digestion keep them warm and fueled through brutal winters. Even so, late winter stress, thin ice and humans kill many each year. (Getty Images)Thermal Features Are Like \u2018An Electric Blanket\u2019<\/p>\n
Along with their built-in winter survival gear, bison will take advantage of environmental perks in Yellowstone, Wuerthner said.<\/p>\n
The ground near the park\u2019s numerous thermal\u00a0features\u00a0stays warm all winter, and bison love to bed down in those spots, he said.<\/p>\n
\u201cIt\u2019s like having an electric blanket underneath you,\u201d he said.<\/p>\n
Bison, like any other wild creatures, must conserve energy all winter long.<\/p>\n
\u201cThey\u2019re taking in a certain amount of calories every day, but not enough to replace the loss of calories through their body functions,\u201d Wuerthner said.<\/p>\n
So, winter isn\u2019t any time to go rushing about, burning off calories that bison can\u2019t afford to lose.<\/p>\n
\u201cBison go into a semi-dormant state in winter. They don\u2019t move around much,\u201d Klemm said.<\/p>\n
When they do move through snow, they go single file, to conserve collective energy, Wuerthner said. \u00a0<\/p>\n
The first bison has to use a lot of energy to break trail, but the next guy behind him has to use less energy, and so on down the line,\u201d he said.<\/p>\n
As with other wildlife, the most perilous time for bison isn\u2019t the depths of winter, but rather, during March and April, he said.<\/p>\n
By then, the animals have burnt through most of their fat reserves, but the nutrient-rich spring forage hasn\u2019t yet sprung forth for them to fatten back up on.<\/p>\n
Even a temporarily elevated heart rate, triggered by people getting too close, can tip the life-and-death balance toward death at that point, Wuerthner said.<\/p>\n
That\u2019s why park officials and biologists urge people to just leave animals in peace during late winter and early spring, he said.<\/p>\n
![\"Wyoming\u2019s](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2025\/12\/Bison-and-snow-GettyImages-155389174-12.13.25.jpg\")
Wyoming\u2019s Yellowstone bison look miserable when caked in snow and frost, but their thick coats, fat reserves and efficient digestion keep them warm and fueled through brutal winters. Even so, late winter stress, thin ice and humans kill many each year. (Getty Images)Other Causes Of Death<\/p>\n
Bison are \u201csupremely adapted\u201d to life in North America, and don\u2019t have any highly effective natural predators, Klemm said.<\/p>\n
\u201cGrizzly bears and wolves don\u2019t kill many bison. They just snipe at the edges\u201d of the herds, he said.<\/p>\n
\u201cHistorically, winter didn\u2019t kill many bison. What killed bison in large numbers was trying to cross frozen rivers in the spring,\u201d he said.<\/p>\n
If the thinning ice collapsed under a herd\u2019s weight, huge numbers of bison would drown all at once, he said.<\/p>\n
Klemm said that in his opinion, the grass in Yellowstone is over-grazed by the dense bison population, and that might contribute to some winter kill.<\/p>\n
Human-caused death is also a big factor.<\/p>\n
In December of 2022, bison wandered on to the highway near West Yellowstone, Montana, and\u00a013 were killed<\/a>\u00a0by a semitruck.<\/p>\n During the nasty winter of 2022-2023, the snow piled up so high in Yellowstone, even the bison decided they\u2019d had enough, and started to leave the park.<\/p>\n Outside the park, that winter roughly 1,000 bison were\u00a0killed by hunters<\/a>, mostly from Native American tribes.\u00a0<\/p>\n