Breeding Cycles and Behavior of Laysan and Black-Footed Albatrosses

Abstract

The breeding biology of Diomedea immutabilis and D. nigripes was studied at Midway Atoll during the 1956-57 and 1957-58 seasons. Both species may first return to the nesting islands at an age of 2 or 3 years, but they do not breed until at least 7 years old. Most pairs breed annually. Black-foots begin to arrive on the breeding grounds about 18 October, Laysans about 1 November. The pair bond is permanent. Both species indulge in a similar ritualized gamosematic and epigamic display, or "dance." Territory is confined to the immediate vicinity of the nest and is used only for mating and nesting; the pairs return to the same territory each year. One egg is laid each season; it is not replaced if lost. The mean laying date is 21 November in the Black-foot, 30 November in the Laysan. The incubation period averages 65.57 days in the Black-foot, 64.44 days in the Laysan. Incubation is continual, the sexes alternating. The male usually relieves the female within 3 or 4 days of laying; the male Black-foot's first span averages 18.16 days; the Laysan's, 22.58 days. Subsequent spans are shorter; the last span averages 7.15 days in the Black-foot, 8.32 days in the Laysan. Hatching usually occurs during the sixth span in the Black-foot, the fifth span in the Laysan. Black-foot chicks are guarded continually by one parent until they reach a mean age of 19.12 days, and intermittantly until 29.79 days; Laysan chicks are guarded continually until 17.18 days, intermittantly until 27.29 days. Newly hatched chicks are fed at least daily by regurgitation; when no longer guarding them, the parents feed tham only every 2 or 3 clays. Parents do not recognize their chicks individually until they are over 10 days old. Newly hatched chicks are altricial, nidicolous, and ptilopaedic; their mean weight is 0.16 kg. At 75 days of age, Black-foot chicks weigh a mean of 3.33 kg., Laysan chicks 2.23 kg. Chicks begin to shed the down at an age of about 75 days. Black-foots fledge at about 140 days, Laysans at about 165 days. There is no "starvation period.".