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In “Extremes,” narrated by David Attenborough, we are swept away to the rarest places in the world to watch snow leopards play in the Gobi Desert of Mongolia, a pack of Arctic wolves hunt giant muskox and hibernating snow frogs mate in the French Alps.

Migratory birds and caribou pass through the plain, which provides important polar bear habitat and is home to other wildlife, including muskox.

But environmentalists say the vast region is home to an array of wildlife, such as polar bears and brown bears, muskox, caribou and millions of migratory birds.

An Alaska state trooper was killed by a muskox attack near Nome Tuesday.

The muskox, which can weigh up to 800 pounds, is a stocky, shaggy, horned, hoofed animal related to goats, antelope and sheep.