S1, E3: Northern Mexico is the country's driest region, dominated by two great deserts - the Sonoran and Chihuahuan. And as you travel west, the conditions get hotter, drier and more challenging. In this film, we unravel the forces that have created this arid world and discover that for the animals who live here, from prairie dog and pygmy owls to rare aplomado falcons, overcoming these conditions can bring rich rewards.