Molt, Maturation of Plumage and Ageing in the Wandering Albatross

Abstract

We compare the pattern and rate of molt and plumage maturation in Wan- dering Albatrosses (Diomedea exulans chionoptera) using prebreeding and breeding birds from South Georgia (S. Atlantic Ocean) and Crozet Islands (S. Indian Ocean). Imma- tures from both sites have a molt cycle which basically alternates molt of outer primaries in one year and inner primaries in the next year. This is similar to, but in its details more complex and flexible than, the molt of the smaller, sympatric Black-browed and Gray- headed Albatrosses (D. melanophris and D. chrysostoma). It differs from the wrap-around molt characteristic of Laysan and Black-footed Albatrosses (0. immmutahilis and D. ni- gripes). Juvenile Wandering Albatrosses have most new primaries when 5-year-olds but even at this age some birds have retained primary 1 since they fledged. Males, but not females, from South Georgia replace more primaries than do Crozet birds. Adults breed- ing for the first time molt fewer primaries than birds breeding 7-l 1 months after a failed breeding attempt; these adults molt on average 6 primaries, similar to successful or failed Black-browed Albatrosses. Successful Wandering Albatrosses, in the 12 months before breeding again, only molt 7-8 primaries on average, in contrast to the 11 primaries molted by biennial Gray-headed Albatrosses in their 16 month breeding interval. The duration of the interval between successive breeding attempts is probably the main constraint on the amount of primary molt that can be accomplished. Failed, but not successful, Wan- dering Albatrosses breeding at Crozet molt more primaries than similar birds at South Georgia. At both sites, the plumage of birds of both sexes gets whiter until about 20 years old. However, South Georgia males are already whiter than Crozet birds at 5 years old (presumably reflecting the faster molt rate of South Georgia birds) and they maintain this difference for the next decade. In contrast, females from both sites mature at similar molt rates until age 10 years (median age of first breeding) when South Georgia birds become and stay whiter than Crozet birds. Plumage maturation rate is much slower in birds from Macquarie Island, but these may not belong to the same subspecies. Conven- tional (Gibson) plumage scores do not provide a reliable means of estimating age of Wan- dering Albatrosses, except in very general (53-5 year) categories. The pattern and ex- tent of molt, however, can age most immature birds of D. e. chionoptera to within one year; we provide a key for doing this.