Maturation of Plumage in the Short-tailed Albatross Phoebastria albatrus Based on Birds of Known Sex and Age on Torishima

Abstract

To facilitate the accurate description of plumage of the Short-tailed Albatross Phoebastria albatrus, we classified plumage into eight components, based on photos taken at a breeding colony on Torishima, Izu Islands. Plumage components of 20 individuals just before fledging and 729 individuals of known sex and ranging in age from 2 to 26 years were scored. The plumage color became more whitish with age. The underbody plumage became white earlier than the upper body, whereas on the thigh, tibia and a posterior part of undertail coverts, dark brown feathers remained even in older age. The upper body turned white from the uppertail coverts towards the front, whereas dark brown feathers remained on the mantle, scapulars and nape, even in older age. The upperwing and underwing were often the same score. The progress of the score was earlier for males than for females. At every age from 3 to 18 years, the summed score of seven components (the underwing score was excluded) was significantly different between sexes, although older age males and females could be considered to have the same score. Individuals with a dark brown mantle, scapulars, rump and uppertail coverts were of age of 5 or less years and had not yet bred, except for a few females. Many individuals started breeding after they had a white part on the rump and uppertail coverts. Males reached final plumage pattern at the age of 8 to 15 years, while females reached final plumage pattern at the age of 11 to 20 years or older.