Inter‐ and intra‐individual variation in the feather coloration of American crows

Avian feathers are remarkably diverse in both form and function. Coloration is among the most studied feature of feathers, but we know relatively little about melanin‐based black coloration. Despite many crows ( Corvus sp.) and other corvids having black feathers that appear uniform to human perception, their feather coloration could play an important role in social communication. We therefore tested whether the coloration of American crow Corvus brachyrhynchos feathers varied by age class and sex, two socially relevant variables. Using a visual modeling approach that accounts for the visual system of American crows, we measured the coloration of American crow feathers from museum specimens. We found that feather coloration varied by age class but not sex. Older individuals had feathers with different hue and more ultraviolet than younger crows. Discriminant function analyses correctly categorized individuals into age classes based on feather coloration with high classification success. The coloration of American crow feathers did not vary based on the time since the last molt and replacement, but did vary with the time since the specimen was collected. The visual modeling approach suggests that crows can discriminate among different feather regions. One region with particularly distinctive coloration properties was a facial mask, which could potentially function to minimize eye glare. Our results suggest that feather coloration in American crows (and potentially other seemingly monomorphic corvids) could reflect underlying qualities of those individuals that are important for social communication.