Summary
Flocks of female Red-winged Blackbirds (Agelaius phoeniceus) were maintained in aviaries to determine whether variation in brightness of epaulette or chin plumage correlated with dominance status in nonbreeding situations. No correlation was found between natural plumage variation and dominance in eight control groups, although dominant females were heavier and in better condition. In two groups in which epaulettes were experimentally brightened on some birds and two groups where some chins were brightened, brightening an individual's plumage had no consistent effect on dominance status. Thus, we did not find any evidence that there is direct selection on female plumage brightness for signalling competitive ability outside the breeding season. We propose that bright plumage in females could be an indirect consequence of genetic correlation with a trait selected for in males.
Methodology
Female Red-winged Blackbirds were caught in a prebreeding spring roost estimated at over 2000 birds located near Inverary, Ontario, approximately 25 km south of the Queen's University Biological Station. For several reasons we felt that birds caught under these conditions (roosting) and at this time of year (spring) were appropriate for testing the hypothesis that plumage brightness is an adaptation for status signalling in nonbreeding situations. First, female Red-winged Blackbirds roost commurlally throughout the nonbreeding season, including the spring. Greenwood and Weatherhead (1982) found that females continued using spring roosts through April and well into May when they initiate breeding. Second, female Red-winged Blackbirds molt following the breeding season and retain that plumage for all of the next year. Although Greenwood et al. (1983) found evidence of a very limited spring molt, this did not involve the epaulettes, so the brightness of a female's plumage does not change over the nonbreeding season. Therefore, birds caught in early spring roosts and studied in early spring should be as representative of the nonbreeding situation as birds caught at any other time during that period.
We caught the birds by placing mist nets in the roost before dusk and capturing birds as they flew in at dusk. We transported females we caught directly to an outdoor aviary at the Biology Station. The aviary was a wooden frame construction enclosed by wire mesh with a fiberglass roof. Wooden partitions separated the aviary into six equal compartments (3 X 2 X 1.5 m).
On the day following their capture, all birds were banded with a single aluminum Fish and Wildlife Service band. Mass was measured to the nearest 0.5 g and wing length (from the bend in the wing to the tip of the longest primary) to the nearest 1 mm. Epaulette length was measured using Vernier calipers as the furthest extent of colouration from the bend in the wing. We measured chin length from the bill to the furthest extent of colouration on the breast with the bird held with its beak pointing perpendicular to its body. We classified chin and epaulette colours using the Munsell(1961) system and colour swatches from Smithe (1975) (Table 1). For the purpose of comparison, epaulette and chin scores of 1 to 4 were classified as bright while scores greater than 5 were considered dull.