Abstract

Plumage is a phenotypic indicator of the evolutionary past; an artifact of avian life histories and social mating systems. Until the past decade, most plumage studies assessed coloration from the subjective human-vision perpective. Plumage coloration has not been extensively studied in Hawaiian honeycreepers, and no studies have utilized objective measurement. This study is the first to investigate and document biogeographical, intraspecifc variation of plumage coloration on an island scale using spectrophotomtery. I measured the breast and rump patches of adult male and female Hawai`i `amakihi ( Hemignathus virens virens) from twelve sites spanning six climatic categories (elevation/rain) on the island of Hawai'i. I tested Gloger’s rule, a biogeographical rule that states birds are darker-pigmented in areas of higher moisture and are more carotenoid-pigmented in drier areas. I found that plumage coloration of Hawai'i 'amakihi varied by elevation and rainfall on the island of Hawai'i, with mixed support for Gloger’s rule. While mean brightness was higher in wetter habitats than in drier habitats, carotenoid pigmentation of males was generally higher in drier habitats. The brightest birds were found at middle elevation in wetter habitats. Sexual dichromatism was more pronounced in the breast region than the rump region, and rump dichromatism decreased as mean annual precipitation increased. The differences in plumage detected by the factor of elevation were analogous to the altitudinal genetic structure documented in `amakihi. My results suggest climate may be viewed as an ultimate factor that plays an important role in the plumage traits of 'amakihi. Sex determination by field key will be improved by revisions that address variation according to locale of 'amakihi capture, and will provide a more accurate estimate of breeding population size and capture sex ratio.