They may all look the same to you, but to penguins, no two are alike. The flightless birds recognize each other mostly by sound. When penguins mate — either for life or at least until the chicks are grown — they sing to learn each other's voices. Once an egg is laid, the male usually keeps it warm, while the mother goes to find food. After a few weeks, the two switch places. When the chick hatches, it immediately begins to call, so the parents will know its voice, too. Today is National Penguin Awareness Day in the US.
Quote: "They have wings but they cannot fly. They are birds that think they are fish." — Morgan Freeman, narrating March of the Penguins