Many of the great rivers of southern Africa start high up in mountain ranges, power their way eastwards across wild forests and grasslands, and eventually empty out into the Indian Ocean. Ride the currents of these powerful bodies of water as they reshape the lives of the wild animals who rely on them.
A look at one of the most famous habitats on the planet, the Serengeti in East Africa, a vast grassland that is home to some of the greatest concentrations of herbivores on the continent. But what is the key to this exceptional grassland that allows such density and diversity?
It is high summer in the Polar Regions, and the sun never sets. Vast hordes of summer visitors cram a lifetime of drama into one long, magical day; they must feed, fight and rear their young in this brief window of plenty. Summer is a tough time for the polar bear family, as their ice world melts away and the cubs take their first swimming lesson. Some bears save energy by dozing on icy sun beds, while others go egg-collecting in an Arctic tern colony, braving bombardment by sharp beaks. There are even bigger battles on the tundra; a herd of musk oxen gallop to the rescue as a calf is caught in a life and death struggle with a pair of Arctic wolves. But summer also brings surprises, as a huge colony of 400,000 king penguins cope with an unlikely problem - heat. The adults go surfing, while the woolly-coated chicks take a cooling mud bath. Nearby, a bull fur seal is prepared to fight to the death with a rival. Fur flies as the little pups struggle desperately to keep out of the way of the duelling giants. Further south, a minke whale is hunted amongst the ice floes by a family of killer whales. The dramatic chase lasts over 2 hours and has never been filmed before. The killers harry the minke whale, taking it in turns to wear it down. Eventually it succumbs to the relentless battering. Finally, comical adelie penguins waddle back to their half a million strong colony like clockwork toys. The fluffy chicks need constant feeding and protection as piratical skuas patrol the skies. When an unguarded chick is snatched, a dramatic "dogfight" ensues.
Patrick follows the grizzly bears that are taking a risk with the weather by leaving their winter dens early. Hungry wolves are struggling to bring down their elk prey in the unusually shallow snow. And for great grey owls, it is the iciness of the snow that is hampering their hunts. Yellowstone's winter is always one of the most brutal on the planet. But 2016 saw weather records broken, and the wildlife was forced to adapt to survive. Kate Humble gets to grips with the science behind this remarkable season, from understanding the importance of the snowpack's structure as the melt begins to uncovering why Yellowstone's unique geology poses problems for some grazer's teeth.