Fig. 1. Male baseline levels of superoxide (bSO) at the end of the carotenoid experiment and its relationship with head chroma change during the corresponding time (mean after – before treatment reflectance measurements; see Materials and methods). Since male natural colour morphs (red, yellow) differ in these trait values, we used measurements standardised for natural colour. The relationship was also statistically significant when we controlled for body condition (r=–0.45, P=0.012, N=31).