EPAULET BRIGHTNESS AND CONDITION IN FEMALE RED-WINGED BLACKBIRDS

Epaulets of female Red-winged Blackbirds (AgPlaius phoeniceus) vary in brightness from brown to bright red-orange. We test predictions of th e hypothesis that condition at the time of molt determines female epau let brightness and that females in superior condition produce brighter epaulets. We compared each female's epaulet with a series of color ph otographs ranked from 1 (dull brown) to 12 (bright red-orange) and con sidered females to have increased in brightness between years if their color increased by at least two ranks. More first-year females than o lder females increased in brightness, more older females increased in brightness after low reproductive effort than after high effort, and m ore first-year females increased in brightness af ter a year of supera bundant food (an emergence of periodical cicadas, Magicicada spp.) tha n after other years. In each case, we expected an improvement in condi tion. We estimated female condition and regressed condition index on d ay of the breeding season. During the breeding season, females that la ter increased in brightness improved in condition relative to females that did not increase in brightness. We confirm a previously reported correlation between age and epaulet brightness, but age does not expla in the relationship between change in brightness and either reproducti ve effort or the emergence of cicadas. We conclude that the most likel y explanation for our results is that condition, at least in part, det ermines epaulet brightness in female Red-winged Blackbirds and that su perior condition is reflected by brighter epaulets. Our results suppor t assumptions of the status-signaling hypothesis and mate-choice hypot heses for the evolution of variable plumage. The best explanation for the evolution of variable plumage among female Red-winged Blackbirds i s that brightness signals status in female-female aggressive encounter s.