Indoor Housing during Development Affects Moult,Carotenoid Circulation and Beak Colouration of Mallard Ducks (Anas Platyrhynchos)

Developmental conditions are known to influence adult phenotypes, including naturally selected traits such as structural size, as well as sexually selected traits such as song and colouration. Biotic environmental factors, e.g., neonatal nutrition and health, are especially known to shape expression of adult traits, but there are fewer investigations on the role of abiotic conditions (e.g., lighting, climate) during the post-natal period. Moreover, the majority of such studies in birds is limited to galliforms and fail to examine sexual signals. We reared mallard (Anas platyrhynchos) drakes under several different husbandry regimes-outdoors with a natural, early-spring photoperiod, or indoors with an artificial, late-spring photoperiod provided by either high-quality or low-quality indoor lights. We tracked growth, moult progress, antioxidant (carotenoid and vitamin A) circulation, and beak colouration (a sexually selected trait) during development and into adulthood. It was found that birds housed outdoors completed moult significantly faster and exhibited more saturated beak colouration at adulthood compared to birds reared indoors under either high or low-quality lighting. Body mass and antioxidant circulation generally did not differ between outdoor-reared birds and those reared indoors on high-quality lighting; however, those reared under high-quality indoor light were heavier than those reared under low-quality light. These results indicate that environmental conditions during ontogeny can impact the development of a sexually attractive phenotype (e.g., faster moult, more colourful bare-parts) in mallards, although the nature of our experimental design does not identify specific causal factors. This finding has implications for the proper husbandry and plumage maintenance of a model avian species.