Planeta Tierra es una aclamada serie de documentales creada por la BBC que nos muestra, en 11 episodios escritos por el prestigioso naturalista David Attenborough, la belleza de nuestro enorme planeta con imágenes nunca antes vistas. 6. "Ice Worlds" UK broadcast 5 November 2006, 6.37 million viewers (24% audience share);[25] US broadcast 1 April 2007 The sixth programme looks at the regions of the Arctic and Antarctica. The latter contains 90% of the world's ice, and stays largely deserted until the spring, when visitors arrive to harvest its waters. Snow petrels take their place on nunataks and begin to court, but are preyed on by South Polar skuas. During summer, a pod of humpback whales hunt krill by creating a spiralling net of bubbles. The onset of winter sees the journey of emperor penguins to their breeding grounds, 160 kilometres (99 mi) inland. Their eggs transferred to the males for safekeeping, the females return to the ocean while their partners huddle into large groups to endure the extreme cold. At the northern end of the planet, Arctic residents include musk oxen, who are hunted by Arctic foxes and wolves. A female polar bear and her two cubs head off across the ice to look for food. As the sun melts the ice, a glimpse of the Earth's potential future reveals a male polar bear that is unable to find a firm footing anywhere and has to resort to swimming — which it cannot do indefinitely. Its desperate need to eat brings it to a colony of walrus. Although it attacks repeatedly, the herd is successful in evading it by returning to the sea. Wounded and unable to feed, the bear will not survive. Meanwhile, back in Antarctica, the eggs of the emperor penguins finally hatch. Planet Earth Diaries tells of the battle with the elements to obtain the penguin footage and of unwelcome visits from polar bears.