Often growing up to 45-50 feet long, humpback whales are some of the world's largest mammals.Migrating up to six thousand miles each year, these huge whales eat the tiniest of sea creatures--krill and plankton.Graceful acrobats, these gentle animals are known for their unusual leaps and movements, and for their beautiful singing.Despite the fact that humans are the only serious threat to them, extensive whaling and increasing pollution in their habitats have endangered their survivial.