Nestling birds attract parental care with begging that often includes the display of colorful gapes and rictal flanges. The evolution of mouth coloration has been attributed to both the enhanced visual conspicuousness of colorful mouths and the potential for color variation to reveal information about nestling quality. For both hypotheses, the visual contrast between the gape and rictal flanges is potentially important to parents' perception of color. We observed, and then quantified with digital photography, striking within-tissue variation in the carotenoid-based coloration of rictal flanges in three passerine species. Yellow flange tissue was most saturated near the gape, indicating higher carotenoid deposition there than in more lateral regions of the tissue. This within-flange color patterning may have important visual consequences and could have evolved in the context of communication between offspring and parents.
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Vol. 125 • No. 2