Variation in Male Plumage and Behavior of the Hawaii Akepa

Abstract

The sexually dichromatic and endangered Island of Hawaii subspecies of Akepa (Loxops coccineus coccineus) is a 10- to 12-g Hawaiian honeycreeper that shows remarkable variation in male plumage coloration, ranging from dull gray to bright orange. We found that this variation is primarily due to a two-year delay in plumage maturation by young males. Second-year males possess a mainly grayish-green plumage that is similar to that of females, and rarely try to breed. Third-year males have a partially orange plumage that is intermediate between that of females and adult males, and competently breed in small numbers. In addition, there are variations within age classes that reflect alternative life histories and perhaps diet. The existence of both femalelike and malelike subadult plumage in a population is unlike North American passerines with delayed plumage maturation, especially cardueline finches, which are considered to be the closest relatives of the Hawaiian honeycreepers. The extreme delay is associated with high survivorship, strong philopatry, and a varied prebreeding competition among males that includes group displays and which lasts for six months or more each year. These characteristics are common in lekking or cooperatively breeding species, but are unusual for a small, monogamous passerine with biparental care.