3/6. The Crossing. It's nature's equivalent to D-Day when one and a half million wildebeest cross a short stretch of the Mara river in search of fresh grazing land. How do the animals contend with Africa's largest crocodiles and a host of big cats? Sean Pertwee narrates the series which unravels the mysteries behind the most dramatic wildlife events. Producers Simon Bell and Richard Chambers ; Series producer Lizzie Green
www.bbc.co.uk/nature