Data from: Female and male plumage brightness is positively correlated among populations of the dichromatic Variable Seedeater

Because studies of plumage coloration often focus on highly elaborate and
conspicuous males, little is known about the factors driving the evolution
of drab plumage in females of dichromatic species. We explored variation
in the color properties of drab female plumage across subspecies of the
Variable Seedeater (Sporophila corvina), and found a correlation between
plumage brightness of male and female plumage patches. This correlation is
consistent with the hypothesis that differences in plumage brightness
among females result, at least partially, from a genetic correlation or
shared developmental pathway with the more conspicuous male plumage traits
that are shaped by sexual selection. Further, we modeled the perception of
female plumage using the avian visual system and found that most of the
variation in color among females is mostly undetectable by birds;
therefore, it is unlikely for such variation to have evolved via direct
sexual selection as a signal for recognition or assortative mating.
Together, these results suggest that variation in S. corvina female color
result from non-adaptive processes. However, we found a reduced variation
on color of dorsal patches compared with that of ventral patches among
females, which could be explained by natural selection operation on
crypsis, reducing the variation on dorsal patches. Finally, we found
little differences in plumage color between adult females and juveniles,
which suggest selection for juveniles to resemble adult females possibly
to reduce aggression from adult males. Additional within-population
studies and behavioral experiments are needed to discern the evolutionary
factors driving variation on S. corvina female color and its function.