All show, no signal? Colour shifts in Atlantic Puffin ornamentation do not predict body condition

Conspicuous ornaments expressed by both sexes are widespread in socially monogamous species, yet their functional significance and links to individual quality remain poorly understood. In birds, brightly coloured bare parts are often hypothesized to act as honest signals of condition, but empirical support for this assumption is mixed. Here, we quantified variation in bill and foot colouration of 73 Atlantic Puffins (Fratercula arctica (Linneaus, 1758)) breeding on Machias Seal Island, Canada, using calibrated digital photography and avian visual models, and tested whether colour saturation was associated with individual body condition. Colour saturation differed strongly among ornamented regions and individuals, and varied between years, indicating substantial spatial and temporal lability in puffin ornament expression. However, across all models, body condition was not a consistent predictor of colour saturation in any region. These results suggest that puffin bill and foot colouration is dynamic and context-dependent rather than a simple honest signal of individual quality. Our findings highlight the need for integrative approaches that link ornament expression with age, physiological state, and reproductive performance to better understand the adaptive significance of mutual ornaments in long-lived seabirds under changing environmental conditions.