On the snowy banks of the Firehole River in northwest Wyoming, a young male bison is facing an end of life decision. He can either lie down in the snow, stained red from his own blood, and let himself be eaten alive by wolves.

Or he can take some control of his last moments and walk a few steps into the icy river, knowing he’ll never walk back out.

Bison are good swimmers, but this one is too exhausted. Just standing up takes everything he has. If he lies down the wolves rush in and start tearing at his hide.

So he struggles to his feet, and the wolves back away, knowing that at some point he’ll lie down and not get up. The river offers the bison an escape, but only in the form of a more merciful death.

We’ve chanced upon this astounding wildlife standoff on a winter snowmobile tour of Yellowstone National Park. The park is less than an hour from Montana’s Big Sky Resort, where my family and I are spending a week skiing.

It’s well below freezing when we arrive in the gateway town of West Yellowstone, although nowhere near the town’s record low of -54C. We shimmy into Arctic-rated jumpsuits, stuff handwarmers into our gloves, and try to pay attention to our guide Roy’s crash course in how to safely drive a snowmobile (squeeze the throttle, point the handlebars, no backflips near the geysers).

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