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.
Part 3: Survival When David Attenborough first visited the Great Barrier Reef in 1957, he considered it the most spectacular place in the natural world and he assumed that it would last forever. Since then the coral has been dying at an unprecedented rate. In this episode he undertakes his most important mission to understand what the next few decades hold for this remarkable community of animals, as well as what is being done to save it. On his journey, David uncovers the remarkable ways in which scientists are trying to preserve the reef and embarks on an ambitious exploration of his own, the deepest dive ever on the reef. But despite the discoveries now being made by scientists and in the reef's furthest reaches, David fears for the future of this incredibly complex and beautiful ecosystem so vital for the world's oceans.
The Cave of Swallows in Mexico is a 400m vertical shaft, deep enough to engulf the Empire State Building. The Lechuguilla cave system in the USA is 193km long and 500m deep with astonishing crystal formations hanging from its chambers. Although often overlooked, caves are remarkable habitats with equally bizarre wildlife. Cave angel fish cling to the walls behind cave waterfalls with microscopic hooks on their flattened fins. Cave swiftlets navigate by echo-location and build nests out of saliva. The Texas cave salamander has neither eyes nor pigment. Unique access to a hidden world of stalactites, stalagmites, snotites and troglodytes brings a wealth of surprises.