Figure 3. As the difference in plumage between males and females
increases, the likelihood of mating (observed number of pairs –
expected number of pairs due to random chance) decreases. Plumage was
quantified by scoring 11 plumage patches on males and females of each
phenotypic class (see Supporting Information for plumage scoring
criteria). Below the x -axis are representative illustrations of
the different pair types (top row: males, bottom row: females),
depicting the male-female plumage divergence with increasing values of
x.
Appendix 1. A plumage scoring criterion. We modified the method of Toews
et al. (2016) to rank Vermivora spp. plumage with the exception
of three edits (denoted using asterisks within table). Intermediate
throat pigmentation (“Thr.”) between a Golden-winged Warbler (Thr. =
0) and Blue-winged Warbler (Thr = 2) should resemble a Brewster’s
Warbler (i.e ., white in color) rather than that of a second-year
male Golden-winged Warbler as in Teows et al. (2016). Additionally,
breast plumage color (“Breast”) and belly plumage color (“Belly”)
for adult male Blue-winged Warblers are bright yellow (rather than
yellow-green) so those plumage categories were extended (from 4- to 5).
All other plumage scoring criteria were identical to those used by Toews
et al. (2016): wing bar width (“W. Bar Wd.”), wing bar color (“W.
Bar. Col.”), nape color (“Nape”), back color (“Back”), rump color
(“Rump”), auricular pigmentation pattern (“Auric.”), supercillium
color (“Super.”), and malar color (“Malar”). A male Blue-winged
Warbler with typical plumage would score 40 using this protocol whereas
a Golden-winged Warbler would score 0.