Is red coloration of male Northern Cardinals beneficial during the nonbreeding season? A test of status signaling

I tested the hypothesis that bright colors may function as signals of status during the nonbreeding season, offsetting possible costs associated with such traits. Male Northern Cardinals (Cardinalis cardinalis) do not defend territories during the nonbreeding season and unfamiliar individuals interact over food resources. To test whether red coloration functions as a signal of status among unfamiliar individuals, I manipulated male coloration by a reddening, a lightening, or a sham control treatment to decouple color from other characteristics that might influence dominance. I observed interactions among males from these treatment groups at a single food source. During the trials, dominant individuals gained mass at a higher rate than subordinant individuals, suggesting a benefit of dominance. There was no effect of treatment or manipulated coloration on the initial or final dominance rank, indicating that males are not using red coloration as a signal of status. However, in the final dominance rank, males with naturally redder plumage were more dominant to those that originally had duller plumage. These results suggest that although red coloration is an indicator of dominance, adult males are not using it alone as a signal of status in controlling food resources.