Luc Jacquet's 2005 emperor-penguin epic. Won Best Documentary Oscar; the highest-grossing nature documentary ever theatrically.
From Wikipedia
March of the Penguins is a 2005 French nature documentary film directed and written by Luc Jacquet. The documentary depicts the yearly journey of the emperor penguins of Antarctica. In autumn, all the penguins of breeding age leave the ocean, which is their normal habitat, to walk inland to their ancestral breeding grounds. There, the penguins participate in a courtship that, if successful, results in the hatching of a chick. For the chick to survive, both parents must make multiple arduous journeys between the ocean and the breeding grounds over the ensuing months.