-- and only in Bermuda. They return in late autumn to their original burrows, court by night and -- after mating -- go back to sea for approximately six weeks before returning again to the Island to have their young.

Females lay one large egg each in the first half of January, which both parents take turns incubating. Chicks emerge in the wintertime and are fed at night on partly digested food from their parents' gullets.

The chicks remain in their burrows throughout the Spring, growing bigger and fatter. By the end of May their feathers are developed, and their parents have returned to sea to spend another summer feeding in the North Atlantic.

With their food source gone, and the fledglings growing ever hungrier, they emerge from their burrows at night to exercise their wings, until finally they take off for their own life at sea. Four to five years later, they too will return to repeat the process of mating and having their young.