The fiercest, strangest, and wildest creatures in the animal kingdom face off in a countdown of the most incredible animal moments ever recorded. Across arid deserts, through dense rainforests, and into the deepest of oceans, witness remarkable scenes of animal activity, from deadly showdowns to wild romances.

The second episode looks at the challenges of hunting in the Arctic, the most seasonal place on Earth. To a predator, seasonal change is a problem. It means that all the parameters of the hunt - the conditions, the strategies, the prey - change too. The only option for the Arctic's top predators, the wolf, the Arctic fox and the polar bear, is to continually adapt to their changing world, exploiting the good times and enduring the bad.

After filming for three years, Planet Earth finally captures the shy Mongolian gazelle. Only a handful of people have witnessed its annual migration. Don't miss the bizarre-looking Tibetan fox, captured on film for the first time. Over six weeks the team follow a pride of 30 lions as they attempt to hunt elephants. Using the latest night vision equipment, the crew film the chaotic battles that ensue at close quarters.

Here, Aleks charts how the Web is forging a new brand of politics, both in democracies and authoritarian regimes. With contributions from Al Gore, Martha Lane Fox, Stephen Fry and Bill Gates, Aleks explores how interactive, unmediated sites like Twitter and YouTube have encouraged direct action and politicised young people in unprecedented numbers. Yet, at the same time, the Web's openness enables hardline states to spy and censor, and extremists to threaten with networks of hate and crippling cyber attacks.

Every year, around the world, seasonal changes transform entire landscapes and draw in millions of creatures as these great events unfold. This fantastic series combines the epic scale of Planet Earth and the intimate, emotional stories of charismatic animals as they struggle to survive. Using state of the art technology, these programmes capture the Earth's most dramatic and epic wildlife spectacles and the intimate stories of the animals caught up in them.
The Great Melt: The summer melt of Arctic ice, opening up nearly three million square miles of ocean and land, provides opportunities for millions of animals, including beluga whales, families of Arctic foxes, vast colonies of seabirds, and the fabled Arctic unicorn, the narwhal. For polar bears, however, it is the toughest time of year. Why? How will they survive? A mother polar bear and her cub make their first journey together onto the sea ice. They are looking for ringed seals, their favourite prey. It is a serious business but the cub just wants to play. The melting ice makes it harder for them to hunt and threatens their survival. In a unique aerial sequence, the migration of narwhal with their distinctive unicorn-like tusks is filmed for the first time. The whales' journey is risky as they travel along giant cracks in the ice. If the ice were to close above them, they would drown. Hundreds of beluga whales gather in the river shallows. They rub themselves on smooth pebbles in one of the most bizarre summer spectacles. Guillemot chicks take their first flights from precipitous sea cliff nests to the sea 300 metres below. They attempt to glide to safety but many miss their target. Their loss is a bonus for the hungry Arctic fox family waiting below. As the melt comes to an end the bears gather, waiting for the sea to freeze again. Two 400kg males square up to each other to spar.

Mammals' ability to learn new tricks is the key to survival in the knife-edge world of hunters and hunted. In a TV first, a killer whale off the Falklands does something unique: it sneaks into a pool where elephant seal pups learn to swim and snatches them, saving itself the trouble of hunting in the open sea. Slow-motion cameras reveal the star-nosed mole's newly-discovered technique for smelling prey underwater: it exhales then inhales a bubble of air ten times per second. Young ibex soon learn the only way to escape a fox - run up an almost vertical cliff face - and young stoats fight mock battles, learning the skills that make them one of the world's most efficient predators.