Meeting Abstract
Male ornaments are thought to honestly advertise the physiological quality of potential mates to females. An important aspect of physiological health is stress response, and there is evidence that increased stress can lead to a number of negative consequences, including reduced expression of ornaments. Eumelanin-based (black) ornaments may be particularly susceptible to the negative effects of high stress hormones (glucocorticoids) as increases in glucocorticoids will reduce the production of POMC prohormone, which is modified into peptides that regulate both glucocorticoid and eumelanin production. Thus, males with lower glucocorticoid levels should be able produce larger eumelanin ornaments. We tested this prediction during the breeding season in a population of common yellowthroats (Geothlypis trichas), in which the size of the black facial mask is a sexually-selected ornament. Mask size is also positively related to body mass, antibody production, resistance to oxidative stress, and variability at the MHC Class II. We measured stress in males by quantifying both baseline and stress-induced corticosterone (CORT), which is the main stress hormone in birds. Stress-induced CORT was measured 30 minutes after capture. We predicted that males with larger masks would have lower baseline CORT and that their stress-induced increase in CORT would be smaller than males with smaller masks. Although mean stress-induced CORT was significantly higher than baseline levels, the change in CORT was not related to size of the eumelanin mask. This suggests that this plumage ornament does not signal stress response during the breeding season.
