Reproductive performance, recruitment and survival of wandering albatrosses Diomedea exulans at Bird Island, South Georgia
The wandering albatross breeding population at Bird Island, South Georgia has declined since 1961 at a rate of 1.0% per annum. Similar declines have occurred elsewhere in the Subantarctic. (2) Using detailed data on recaptures of birds ringed as chicks in 1958, 1962, 1963 and 1972 onwards, we examine the relative importance of changes in breeding success, breeding frequency and survival and recruitment rates to the decline since 1976. (3) Breeding success (average 64%) has increased by 1.2% per annum, with increases in hatching and fledging success about equally responsible. Breeding frequency has remained constant, except that higher breeding success means more birds breeding biennially. Of successful breeders, 72%, 8% and 6% breed 2, 3 and more years later, respectively; of unsuccessful birds, 68%, 14% and 6% breed 1, 2 and more years later. (4) Recruitment to the breeding population has decreased from 36% (of a cohort) in the 1960s to 30% nowadays; average age of first breeding has also decreased. (5) Adult survival averages 94%; females have a 2% significantly lower rate than males; survival in the 1960s was probably 1-2% higher. (6) A demographic model is developed which closely matches the observed changes and gives rates of population decrease between 0.9 and 1.1% per annum. (7) The causes of the population decrease must operate mainly outside the breeding season (because of high breeding success); the few recoveries of birds of known status support this. Earlier suggestions that incidental mortality due to fishing activity in lower latitudes is important are strongly reinforced by new data (direct observations, ringing recoveries) on birds killed during long-line fishing for tuna. Annual mortality rates may exceed 2-3% of Bird Island adults and 15% of juveniles