What is the name of the penguin’s annual fasting period while it replaces its feathers?

A penguin’s annual fasting period while it replaces its feathers is called a catastrophic molt.

During this molt, a penguin sheds and replaces its entire plumage over a short period rather than replacing feathers gradually. New feathers do not initially provide the waterproof protection needed for swimming, so the bird remains on land and cannot forage normally.

Before coming ashore, a penguin feeds heavily and builds energy reserves. The fast commonly lasts around two to three weeks, though its length varies by species and individual. Once the new waterproof coat is ready, the penguin returns to the sea.

“Catastrophic” describes the sudden, complete nature of the plumage change, not a disaster. This process differs from the gradual feather replacement seen in many other birds. Penguins must time it carefully because their survival depends on both stored body energy and the completion of the new insulating coat.