Emperor penguins cross a treacherous frozen sea to reach their breeding grounds. Rockhoppers brave the world's stormiest seas only to come ashore and face a daunting assault up a 300-foot cliff, hopping most of the way up. Tropical Humboldt penguins negotiate predatory sea lions and vampire bats to reach their desert nests. The hard work for all the penguins finally pays off when their tiny, vulnerable chicks begin to hatch.