The clutch is a single egg, usually pure white, sometimes with some reddish-brown spots that soon disappear. The average size of the egg is , and it weighs , of which 6% is shell. If an egg is lost early enough, a replacement may be laid on rare occasions. This is very unusual for tubenoses. The eggs are incubated by both parents for 38–50days, the longer periods arising when the eggs have become chilled through adult absence. One adult typically spends three days at a time on the egg while its partner feeds at sea. The chicks are altricial and covered with silver-grey down, and are fed by both parents with their regurgitated oily stomach contents. The adults do not normally stay with the chick after the first week, visiting only to bring food. After about 50days, the chicks are fed less regularly, sometimes with gaps of several days, and the parents may stop visiting completely shortly before the chick leaves the nest. The chicks fledge about 56–86days after hatching, and receive no parental support after leaving the nest hole.