The subject of the second programme is the annual salmon run on the west coast of North America. Hundreds of millions of Pacific salmon return to the mountain streams in which they were born, where they will spawn and then die. Their passage upstream is fraught with danger, from rapids, waterfalls and hungry grizzly bears. The programme begins at the arrival of spring, with a grizzly mother leading her cubs down from their winter den in the Alaskan mountains. The bears congregate in the forested valleys, where they forage for whatever food they can find. Survival is tough for all, as shown by a pack of hungry wolves attacking an adult grizzly. It is not until July that the salmon arrive in great numbers. Those that make it past the bears risk becoming trapped in shallow reaches as the water level subsides. Relief comes as a summer storm replenishes the streams, triggered by moist ocean air rising over the coastal mountains. As they reach the spawning grounds, the salmon change body shape and colour in preparation for spawning. When it is over, the fish are close to exhaustion and they die en masse, providing an easy meal for birds and lingering bears. Their deaths are not in vain, for the nutrients from their decaying bodies help to fertilise the soil, sustaining the forests of tall pines. The diary piece, "Close Encounters of a Grizzly Kind", reveals how footage of the bears fishing using their feet was obtained.
Nature's Great Events is a wildlife documentary series made for BBC television, first shown in the UK on BBC One and BBC HD in February 2009. The series looks at how seasonal changes powered by the sun cause shifting weather patterns and ocean currents, which in turn create the conditions for some of the planet’s most spectacular wildlife events. Each episode focuses on the challenges and opportunities these changes present to a few key species. Nature's Great Events was produced by the BBC Natural History Unit in association with the Discovery Channel and Wanda Films. The British version of the series was narrated by David Attenborough. In the USA, the series was shown under the alternative title Nature's Most Amazing Events beginning on 29 May 2009 and was narrated by Hasani Issa. The title Nature's Great Events was previously used by Reader's Digest for a unrelated VHS series released in 1996. Source