Male stress response is related to ornamentation but not resistance to oxidative stress in a warbler

1. Ornaments are thought to honestly signal individual quality to potential mates. Individual quality may include the ability to cope with stress through the production of glucocorticoids (GCs), which help to redirect resources from growth or reproduction to survival during an acute stress response. However, elevated levels of GCs may also increase oxidative stress and reduce immune function. Thus, an important question is whether high quality individuals, with more elaborate ornaments, signal their ability to produce a strong stress response and mitigate some of the negative effects of doing so through higher resistance to oxidative stress. 2. We tested whether ornamentation and resistance to oxidative stress were related to the magnitude of the increase in corticosterone (CORT), the main GC in birds, during an acute stress response in common yellowthroats (Geothlypis trichas). Males in this species have two plumage ornaments, a black (eumelanin-based) facial mask and a yellow (caroten...