'It was a real battle of the titans': The moment one polar bear took on a walrus herd

Twenty years on, relive the iconic scene from Sir David Attenborough's Planet Earth that changed our understanding of how polar bears adapt to survive.

It is an extraordinary scene: a lone male polar bear attacks hundreds of walruses – circling them and persistently trying to penetrate their six-inch blubber to secure a long-awaited meal.  

Using the foggy landscape as cover, he approaches a walrus colony. The adult walruses work as a team, pushing their young into the centre, and creating a barrier of blubber and hide. The bear begins its ambush tentatively, jumping up onto a walrus' back to find a chink in the armour to reach the pups. He targets a female walrus, repeatedly biting her neck. She fiercely shields her pup, and his claws and teeth are unable to pierce through her thick hide. The herd start to flee into the sea, and the bear becomes increasingly desperate, turning to fight the adult walruses.

His chance of securing his first meal in months is slipping away. The bear latches onto an adult walrus, but the flailing animal uses its immense power and manages to slip from his grasp.

At the end of the sequence we see the bear limping, deafeated, and gravely wounded from the walruses' tusks.

You can watch the video below to see the ferocious battle unfold.

This dramatic sequence was captured by award-winning underwater cinematographer Adam Ravetch in 2004. He spent two years in the Arctic, filming footage for the Ice Worlds episode in Planet Earth, the landmark natural history documentary series presented by Sir David Attenborough.

It was a moment of high drama in the natural world, which would become characteristic of the Planet Earth series. But this was more than a moment of striking television. This battle was a symptom of the ways polar bears were adapting to survive in some of the world's harshest conditions.

In his second year of filming, Ravetch and his guide were two weeks into their third "stake-out" in a remote part of the Arctic Ocean, when it became clear that their food supplies were thinning. Ravetch decided to stay on location alone.

Soon enough, an exhausted polar bear appeared after a long swim, drawn in by the "pungent smells emanating from the island" as Sir David narrates in the episode. The bear hadn't eaten in months and was forced onto land in search of food.

One small obstacle lay ahead, however. "It had to [get past] me to get to the walrus," Ravetch says. The bear circled the small self-built cabin which he perched on top of (dubbed "the coffin"), before launching its full-blown attack on the walrus herd with Ravetch close behind, his camera in tow. 

"I've never felt more in danger and alive in my life," he recalls. Polar bear attacks on humans are rare, but when they do occur they are often fatal.

But Ravetch knew he was witnessing something remarkable. Polar bears typically target walrus cubs and rarely attempt to take on adult walruses. They had never been documented being injured by a walrus herd. "I thought the bear would […] grab a walrus calf successfully in minutes, but this was brand new behaviour to see the walrus fight back and win," Ravetch says. The length of the sequence also meant that he was able to capture multiple failed attempts by the polar bear.

The walruses took a while to escape into the sea, allowing Ravetch to film this extraordinary behaviour at length and in intimate detail. It was "the first time we so intimately saw........

© BBC