Plumage Ornaments Signal Male Physiological Quality in Common Yellowthroats

Abstract

Elaborate ornaments are thought to honestly signal quality to potential mates. These ornaments may signal a variety of physiological processes that affect health and fitness. I examined the relationship between ornaments and physiological quality in a bird, the common yellowthroat (Geothlypis trichas). Male common yellowthroats have two plumage ornaments, a black (eumelanin-based) mask and a yellow (carotenoid-based) bib. Males with larger masks are preferred by females for both extra-pair and social mates. I found that both the mask and the bib of male common yellowthroats honestly signal their ability to resist oxidative stress. Males with larger masks and more colorful bibs also produce a greater amount of corticosterone, a hormone that releases stored energy and induces adaptive behavioral changes, during a short-term stress response. This suggests that these ornaments signal how well males cope with stressful situations. In contrast, neither the mask or the bib signal the infection intensity of haemosporidian parasites across males in the population. However, haemosporidian infection intensity was not related to overwinter survival or body mass, suggesting that these parasites may not be very costly. Together, these results suggest that both melanin- and carotenoid-based plumage ornaments honestly signal male physiological quality in common yellowthroats.