Both parents take turns bringing food to the chicks, which happens two to three times daily, and most frequently in the morning and early evening. Chicks remain in the burrow and rely on their parents until they are fledged, which usually happens 45-55 days after hatching. There is no post-fledging parental care, and the puffling first leaves the nest for the open sea alone and at night. Young puffins usually do not return to the colony for almost two years, spending all their time at sea. Puffins become sexually mature at the age of three, but most do not mate until they're four.
Juveniles moult during their first winter at sea, and again the following autumn.
Adult puffins moult completely following the breeding season, and partially before breeding. When faced with an intruder close to their burrow, puffins open their bills and lower their head, and may follow this action with bill grappling or kicking. They have a limited range of calls, including a low grumbling noise heard usually from underground in breeding colonies. Chicks often peep to indicate that they want food. When conspecifics fight, they spread their wings, open their mouths wide, stomp their feet, and wrestle with their opponents.