Incubation begins when the first egg is laid. Subsequent eggs are laid one to three days apart; clutches have 2-4 eggs. The female usually takes on most of the responsibility of incubation, seldom leaving except to feed. The male then takes over incubation until her return. Incubation takes from thirty-four to forty days.
The first chick to hatch has an advantage over the siblings which hatch a day or two later. The first chick grows quickly and can dominate the nest. In years when the food supply is low, the dominant first chick can usurp the available food supply to the peril of the smaller siblings. This insures that at least one of the year’s brood might survive. The chicks are brooded by the female for approximately ten days. The young are too large to fit under her by this time. She will continue to protect them by covering the young with her wing.
Division of Labor
The male, dedicated to providing for his family, does all of the hunting until the chicks are six weeks old. The male delivers the fish to the female on the nest who tears off pieces to feed to the young. At three to four weeks of age the chicks start to exercise their wings by holding onto the edge of the nest and flapping their wings. Mom then moves to a near by perch to guard the nest. The female may leave the nest to hunt when the chicks are six weeks old. The young start to feed themselves at this time.