The egg is incubated for 42-47 days while the parents take turns incubating. The off-duty bird goes out to sea to feed. The chick is hatched in July or early August, and for the next 45-55 days until it is fledged, it remains in the burrow while its parents take turns feeding it and standing watch. After five days or so the chick can keep itself warm, and both adults leave to gather food for the chick. As Fall approaches, there are gradually fewer birds at the colony.
Adults leave for the winter as chicks fledge and grow on the open ocean.
Most birds spend the winter far offshore in the north Pacific Ocean and do not venture near land. Young puffins remain on the open sea during the summer of their first year. When they are 2 years old they visit the colony during the summer. At 3, puffins are mature enough to breed, but it is only at 4 that they are certain to breed. Some banded birds have been found still breeding at 10 years old.