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

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 ( GC s), such as corticosterone ( CORT ), which help to redirect resources from growth or reproduction to survival during an acute stress response. However, elevated levels of CORT 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. We tested whether ornamentation and resistance to oxidative stress were related to the increase in CORT during an acute stress response in a warbler, the common yellowthroat ( Geothlypis trichas ). Males in this species have two plumage ornaments, a black (eumelanin‐based) facial mask and a yellow (carotenoid‐based) bib. We measured the increase in CORT in response to the stress of capture and handling. Males with more elaborate ornaments (larger masks and more colourful bibs) had a greater increase in CORT during an acute stress response. However, the increase in CORT was not related to resistance to oxidative stress. These results suggest that both melanin‐ and carotenoid‐based plumage ornaments can signal the ability of a male to cope with stressors through a greater increase in CORT . Thus, the association between ornamentation and stress‐induced CORT is not likely due to a mechanism specific to a particular colour (melanin or carotenoid), but instead may result from more general interactions between CORT and health or condition. A plain language summary is available for this article.