Mortality and Survival in the Laysan Albatross, Diomedea immutabilis

A 13-year study of 27,667 banded Laysan Albatrosses, Diomedea immutabilis, on Midway Island, North Pacific Ocean, provided specific mortality rates for each stage of the life cycle. Egg loss among 6,543 nests averaged 3 to 6 percent in the 1st month of incubation and reached 25 percent during the 2nd month in some seasons. Chick losses ranged from 3 to 17 percent of the eggs laid and occurred more or less evenly from hatching to fledging. Most egg losses were occasioned by desertions by adults, and most deaths of chicks occurred when one or both parents died. Approximately 3.5 percent of 4,492 banded, departing fledglings died of starvation and exhaustion on the beaches. Losses to sharks in the nearby waters were thought to increase fledgling mortality to perhaps 10 percent before the surviving young birds reached the open sea. A mean 6.8 percent of 7,000 juveniles were lost in each of the first 4 years at sea, but in each of the next 4 years, when the birds were more experienced and had spent more time in the colonies where there were no natural predators, annual mortality averaged only 1.8 percent. Young breeders had a mean annual mortality of 3.7 to 4.0 percent in their first nine breeding seasons, whereas a total of 3,305 breeders of all ages had a mean annual mortality of 5.3 to 6.3 percent. There was no consistent sexual variation in mortality of breeding birds, but in 2 years of low breeding populations females experienced greater losses. Prior to the 14th year of life, the stresses of reproduction were perhaps more significant mortality factors than was age. Age may have been a factor after this, but not until the years after 20 was there any indication of increased mortality. Approximately 40 percent of the breeding albatrosses lived to a minimum of 12 years, 30 percent to 14 years, 25 percent to 16 years, 20 percent to 18 years, and 13 percent to 20 or more years. Laysan Albatrosses may have a breeding life expectancy of some 16 to 18 years. THE PURPOSE of this investigation was to determine specific mortality rates for each stage of the life cycle of the Laysan Albatross, Diomedea immutabilis. Underlying this purpose was my desire to present high quality, primary data for comparative use by statistically minded ornithologists and "model-building" ecologists in general. As Hickey (1972: 27) noted, the lack of good, primary information is all too evident in many reports. [ Manuscript received 28 September 1974. 2 Southern Illinois University, Carbondale, Illinois 62901. Present address: Fenwood Toft, Triplett, Missouri 65286. No attempt is made here to assess in depth all the factors causing mortality or to theorize about the implications of differential mortality upon the dynamics of the species. Almost nothing is known of the life of the Laysans at sea, where most of their lives are spent, and emphasis must lie on the mortality factors on land. The Laysan Albatross is an excellent subject for studies of survival. From hatching it is firmly attached to a site within the colony, and it is predictably present there after the age of approximately 4 years. It occurs in large numbers on the breeding grounds, is docile, not