Penguins lose all their feathers at once in a process called a catastrophic molt.

Penguins need a perfectly smooth and dense layer of feathers to stay warm in freezing water. If they lost feathers slowly like other birds, gaps in their coat would let cold water reach their skin. To prevent this, new feathers grow underneath the old ones and push them out in large clumps.This process takes about two to four weeks depending on the species. Little Blue Penguins lose nearly half of their body weight during this time. They cannot enter the ocean to eat because their new feathers are not yet coated in waterproof oil. This oil comes from a special gland near their tail called the uropygial gland.Before the molt begins, penguins eat extra fish to double their body weight. Their bodies use this stored fat for energy while they wait on land. A penguin's metabolism doubles during the molt to provide the energy needed to grow thousands of feathers quickly. Once the new feathers are ready, the penguin returns to the sea to hunt again.