They share the same valleys in Yellowstone, and they have done for thousands of years. One is North America's heaviest land animal, a 900 kg wall of muscle built to shrug off wolves. The other is the continent's most powerful predator, with a bite that crushes bone. Tourists film their standoffs every summer, but the real balance of power is more surprising than the highlight reels suggest. Here is what the measurements and the documented encounters actually show.
Bison bison
Ursus arctos horribilis
Every category uses median adult measurements. The highlighted cell shows which animal holds the measurable advantage -- not the guaranteed winner of an encounter, which in this matchup depends heavily on motivation and circumstance.
| Category | Bison | Grizzly Bear | Advantage |
|---|---|---|---|
| Raw mass | 540 -- 900 kg | 180 -- 360 kg | Bison (2 -- 3x) |
| Top speed | 55 km/h | 56 km/h | Near tie |
| Primary weapon | Horns + 900 kg charge | Claws + 1,160 PSI bite | Grizzly (versatile) |
| Bite force | Negligible (grazer) | ~1,160 PSI | Grizzly |
| Predatory intent | None (defensive only) | Apex predator | Grizzly |
| Agility / turning | Surprisingly nimble | Higher (climbs, pivots) | Grizzly |
| Defensive armor | Thick hide, dense shoulder hump | Heavy fat + muscle | Bison |
| Stamina | Herd-grazer endurance | Burst predator | Bison |
| Numbers advantage | Herd defense | Always alone | Bison |
| Encounter outcome (wild) | Usually unbothered | Usually backs down | Context-dependent |
A mature bull American bison weighs two to three times what an average male grizzly does. That is not a small edge -- it is the single most important number on this page. A 900 kg animal moving at 50 km/h carries an almost unstoppable amount of momentum, and a bison's charge is delivered head-down through a reinforced skull and horns into the most vulnerable part of any attacker. Yellowstone tourists have been gored and thrown several metres by bison that weighed less than this. A grizzly absorbing a full charge is taking the kind of impact that breaks ribs and snaps spines.
The bison also fights from the front, which suits it. Its thick hide and the dense muscle of its shoulder hump make the most-attacked area the hardest to injure. And crucially, bison rarely fight alone -- a herd will close ranks around calves, presenting a wall of horns that even a determined predator will not push through.
Mass loses some of its meaning when only one animal in the fight actually wants to kill the other. The bison is a grazer with no predatory instinct, no killing bite, and a defensive playbook built for wolves, not for a 1,160-PSI jaw and ten-centimetre claws. The grizzly bear is the most powerful land carnivore in North America, with the strength of several adult humans concentrated in its forelimbs and a bite that crushes the femurs of elk for the marrow.
When a grizzly commits to a bison, it does what predators do: it avoids the horns, attacks from the flank or rear, and uses its claws and weight to pull the animal down and reach the spine or throat. A grizzly is also more agile than its bulk suggests -- it can pivot and accelerate faster than a bison can re-orient its mass. Against a calf, an injured bull, or a bison weakened by a hard winter, the bear's tools are decisive.
Unlike most "who would win" matchups, bison and grizzlies meet constantly in the real world. Yellowstone is the natural laboratory, and decades of observation show a clear pattern: most encounters end with no fight at all.
The overwhelmingly common outcome. Bison and grizzlies graze and travel in the same meadows daily. Large male bears walk through bison herds routinely; healthy adult bison ignore them. Neither animal wants the injury a fight would cost.
No contestWhere grizzlies genuinely win. In spring, bears target bison calves -- the herd defends, but a determined grizzly can separate and take a vulnerable calf. This is the most frequent form of successful bison predation by bears.
Grizzly favoredDocumented in Yellowstone footage: a grizzly pursuing a bull already injured or exhausted (often after the rut or a hard winter). Against a compromised animal the bear's predatory toolkit prevails, sometimes after a prolonged battle of attrition.
Grizzly favoredThe matchup people imagine, and the one grizzlies avoid. Faced with a charging, uninjured adult bull, grizzlies very often back down rather than risk a goring. A 900 kg defender with horns is simply not worth the gamble.
Bison favoredThis matchup splits cleanly by circumstance, which is exactly why it is so widely argued. If a grizzly chooses the fight on its own terms -- a calf, an injured bull, an ambush from the flank -- the bear's predatory advantages win. That is why grizzlies are a real, documented predator of bison.
But a healthy adult bull bison meeting a grizzly head-on is a different animal entirely. The two-to-three-times mass advantage, the horns, the head-down charge, and the herd behind it tip the encounter the bison's way -- and the grizzlies themselves agree, because they routinely walk away from exactly that scenario.
The short version: grizzly as the hunter picking its moment, the bear wins. Healthy bull defending itself, the bison wins -- and the bear usually knows better than to try.
