Ultraviolet crown coloration in female blue tits predicts reproductive success and baseline corticosterone

A growing number of studies provide evidence that female plumage coloration is indicative of individual quality and can influence male mate choice. In blue tits (Cyanistes caeruleus), both sexes exhibit bright ultraviolet (UV)-reflectant crown feathers, which have previously been shown to be attractive to the opposite sex. In males, there is evidence that UV reflectance of the crown feathers is an honest signal of quality in this species, but it is unclear whether this is the case for females. To address this, the UV signal (an index of relative UV reflectance specific to the visual sensitivities of the blue tit) of mothers was measured during brood rearing for 3 years (2008–2010) and related to indices of reproductive success, that is, lay date, clutch size, and number of chicks fledged and maternal state, that is, body condition and baseline corticosterone (CORT). Maternal UV signal was unrelated to clutch size but was positively correlated with number of chicks fledged in 3 years. Maternal UV signal was also negatively correlated with lay date, but this was not consistent across years. In addition, maternal UV signal was negatively correlated with baseline CORT in all years but was not predictive of body condition. Taken together, these results provide evidence that female plumage coloration is indicative of female quality and may serve as a signal for mate choice. Further, it provides novel evidence that maternal baseline CORT is associated with UV plumage signal in free-living birds and may be an important mechanistic link between an individual’s ornamentation, state, and reproductive performance.