The lives of animals and plants are dominated by the sun and fresh water which trigger seasonal journeys. The latest technology and aerial photography enable the Planet Earth team to track some of the greatest mass migrations. In the Arctic spring, a mother polar bear and cubs emerge from their winter den. They have just two weeks to cross the frozen sea before it melts and they become stranded. Share the most intimate and complete picture of polar bear life ever filmed. Further south, time-lapse cameras capture the annual transformation created by the Okavango floods.