Each year, bar-tailed godwits undertake the longest unbroken migration of any bird, flying from their breeding grounds in the Arctic to Australia and New Zealand and back again. They follow invisible pathways -- pathways that have been followed for thousands of years -- while braving hunger and treacherous conditions to reach their destination. In Circle, Jeannie Baker follows the godwit's incredible flight, taking us over awe-inspiring scenes as the birds spread their wings above such beautiful landmarks as the Great Barrier Reef and China's breathtaking cityscapes.