After their first few weeks of life, emperor penguin chicks are no longer brooded by their parents around the clock and they begin to form creches where they keep each other warm by huddling together, just like adults do in mid-winter. When parents return from the sea they head for the creches to pick up their chicks, which they recognize by sound rather than sight. In this image you can see two adults trying to figure out which of the chicks are theirs.