The carotenoid-based ornaments displayed by many birds often play key roles in social and sexual signalling, revealing information about individual quality. Understanding the mechanisms of coloured trait production and maintenance requires an accurate description of their composition and of the physiological pathways involved in their expression. Carotenoid-based colouration has been extensively studied in birds, but such information is often lacking for coloured integuments other than feathers, such as fleshy carotenoid based ornaments. Authors report the carotenoid composition of the combs of the red grouse, a sexual trait that honestly reveals individual quality. It was found that comb pigmentation was primarily the result of two red ketocarotenoids (astaxanthin and papilioerythrinone), which are synthesised from their dietary precursors (zeaxanthin and lutein) directly at the comb integument. These red ketocarotenoids are largely deposited esterified with fatty acids. Astaxanthin concentration in the comb was found to negatively correlate with retinol levels but positively correlate with tocopherol levels. Considering evidence from this and other studied species, authors suggest that carotenoid esterification is a characteristic of coloured fleshy integuments, probably affecting pigment stability and colouration in living tissues, with subsequent effects on their signalling role and maintenance costs. Honest signalling via comb colouration appears mostly related to potential allocation trade-offs of some specific dietary precursors or to the capacity of individuals to manage the redox reactions interfering with carotenoid metabolism. informacion[at]ebd.csic.es: Pérez-Rodríguez et al (2016) Carotenoid profile and vitamins in the combs of the red grouse (Lagopus lagopus scoticus): implications for the honesty of a sexual signal. J Ornithol 157:145–153 DOI 10.1007/s10336-015-1261-y