Molt and dichromatism scoring
We scored the extent of prealternate molt and plumage dichromatism using a combination of specimen examinations and literature review. All specimens were examined at the LSU Museum of Natural Science. We used a combination of collection date, data from specimen labels, and known molt patterns (Pyle 2007) to classify individuals by age, sex, and molt stage. Species or life stages not available at the LSUMNS were scored from the literature (Pyle 2007) or visual examination of published photographs of plumages (Dunn and Garrett 1997, Stephenson and Whittle 2013). We defined a dichromatic region as a region with visible color or pattern differences between basic and alternate plumage. We scored dichromatism in feather regions as follows: 1 = region completely dichromatic, 0 = no dichromatism in region, and 0.5 = and partial dichromatism or intraspecific variation. In some species, extent of molt and dichromatism differs between the first prealternate molt and definitive prealternate molts. In these cases, we considered only the definitive prealternate molts (Wolfe et al. 2014). We scored molt extent using the same museum and literature resources, through examination of molt limits (Pyle 1997a). For each body region (Fig 2f), we scored molt as follows: 1= complete replacement of the feathers in the region, 0 = molt absent from the region, and 0.5 = either partial replacement of the feathers in that region, or intraspecific variation in extent of molt.