S1, E3: Borne of suffering, desperation, and starvation, every migration is a death-defying journey, filled with countless obstacles. Science of Great Migrations will go behind breathtaking images of migration and show how scientists learn from and study these magnificent spectacles of nature. The iconic migration of wildebeest in the Serengeti; the 1,800 mile flight path of the monarch butterfly; the two-month pilgrimage of the southern elephant seal off Patagonia; and the perilous journey of African elephants in Mali together give scientists a look into this dangerous world of migration. Advances in scientific technology and data collection are revealing a new understanding of animal decision-making, swarm dynamics and the inner workings of a herd, flock or pod.