Narrated by Peter Firth, the series takes a look at a year in the life of Yellowstone National Park, examining how its wildlife adapts to living in one of the harshest wildernesses on Earth.The series was one of the most popular titles at BBC Worldwide's annual market for international clients with pre-sales to nine territories including Spain (Canal+), Germany (WDR), Russia (Channel 1) and Italy (RTI).Stabilised camera mounts also enabled the team to capture natural animal behaviour from the air, as well as dramatic, wide angle landscape shots.By the end of March, winter has loosened its grip, and the emergence of grizzly bears from hibernation in their mountain dens signals the approach of spring.By June, the blooming wildflower meadows attract calliope and rufous hummingbirds, but when a summer blizzard blows in, the birds must turn to sugar-rich tree sap to survive.Yellowstone cutthroat trout mass in shallow streams ready to spawn, but they make easy prey for otters and osprey.Lightning can spark fierce wildfires, but the short-term devastation is part of the ecological cycle and helps the lodgepole pine forests regenerate.Meanwhile, grizzly bears converge on the high mountain slopes as they seek out an unusual food source: army cutworm moths, which arrive in their millions from the prairies.The wolf's return has restored the natural balance of Yellowstone: elk no longer graze along the river banks, leaving more willow saplings for beavers.