Functional significance of sexual dimorphism in Wandering Albatrosses, Diomedea exulans

1. The investigation covered whether sexual dimorphism could affect flight performance in a manner that is consistent with differences in at-sea distribution of male and female Wandering Albatrosses, Diomedea exulans Linnaeus. Adult morphology was also compared to near-fledged chicks to assess whether morphological differences are consistent with different at-sea distributions of adults and fledglings. 2. Body girth, mass, wing span and area were measured on 24 females (16 adults and 8 chicks) and 32 males (20 adults and 12 chicks) breeding in the Crozet Archipelago. 3. On average, adult males had longer wings (4%, 311 +/- 4 cm) with 6.8% more area (6260 +/- 270 cm(2)), but were also 20.4% heavier (9.44 +/- 0.59 kg) than adult females. As a result, wing loading in adult males was 12.1% greater than adult females. 4. When compared with adults, total wing area of chicks was lower resulting in higher wing loading because of the incomplete growth of chicks at the time measurements were collected. However, projected chick growth to fledging indicates that wing loading would be lower in fledglings than adults. 5. Because wing loading determines flight speed, it is conceivable that windier regions of the sub-Antarctic/Antarctic are more optimal for male albatrosses because they have higher wing loading. Conversely, wing loading is lower in adult females and fledglings, which could make them better adapted to exploit lighter winds of the subtropical and tropical regions. Thus, size dimorphism may have a functional role in flight performance that influences the at-sea distribution of adult and fledgling Wandering Albatrosses.