Sherpas hold a ceremony to ask Mount Everest permission to climb before embarking on their journey.

Sherpas hold a tenuous group meeting at Everest Base Camp immediately after the devastating avalanche in April 2014.

Sherpa, part of Elevation Weekend, premieres Sat Apr 23 at 9/8c.

A southern sea lion tires of chasing gentoo penguins in the surf and attempts to run one down on the beach. Both champion swimmers, these two are anything but graceful on land.

A pack of northern gray wolves harass and then attack a herd of wood bison. This is the first time wolves have been filmed hunting bison, both from the ground and from the air.

Frozen Planet represents the most extensive filming of the Antarctic interior ever attempted. Series Producer Vanessa Berlowitz explains how this was done from a twin engine airplane.

A mother polar bear escorts her cubs across the ice, but the youngsters are too interested in playing, in this scene from Frozen Planet.

An Adelie penguin turns to a life of crime to build the perfect nest on Antarctica's Cape Crozier.

The Frozen Planet film crew went to incredible lengths to film penguins in Antarctica. Two went a bit stir crazy filming an Adelie penguin colony, while others braved freezing temperatures to capture emperor penguins.

The Arctic's woolly bear caterpillar freezes solid every winter, the natural antifreeze in its body keeping it from dying. It takes 14 years before it has eaten enough to become a moth.

Tracking killer whales in Antarctica would be impossible without satellite tags. These tags allowed the Frozen Planet film crew to pinpoint the location of the orcas, and film their behavior for the series.

An Antarctic fur seal pup's life hangs in the balance as two males battle for mating rights in the middle of the colony. Will the pup survive or be crushed by the combatants?

An older caribou bull is forced to fend off a herd of young males intent on stealing his mate. Will he stop to fight or keep up with the chase? He has to play his cards right, as the victor will be the new "boss."

Arctic wolves attack a musk ox calf on Canada's Ellesmere Island, but the herd rushes to its defense. When threatened, musk oxen will form a defensive circle around the calves, the sick and the elderly.

In the Canadian Arctic, massive packs of gray wolves hunt the continent's largest land animal: wood bison. The Frozen Planet film crew endured freezing temperatures to capture these unprecedented hunting scenes.

A polar bear gives birth in her winter's den. The cubs are born blind and tiny. A polar bear's milk is nine times richer than our own, so the cubs will double in weight every two weeks.