What is the term for the annual replacement of a penguin’s entire feather coat?

The annual replacement of a penguin’s entire feather coat is called a catastrophic molt.

During this molt, a penguin loses and replaces all of its feathers over a relatively short period. Unlike many birds, it cannot maintain normal waterproof insulation while the old feathers are being replaced. As a result, penguins generally remain on land and do not forage at sea during the process.

Before molting, a penguin usually feeds intensively and builds up energy reserves. The new feathers must grow quickly because waterproof plumage is essential for cold-water swimming. The timing varies among species and populations, often occurring after the breeding season.

“Catastrophic” describes the sudden, complete nature of the molt, not a disaster. It is different from the gradual partial feather replacement seen in many other birds. A penguin’s bright breeding plumage and worn post-breeding appearance can therefore change noticeably across the year.