Antioxidant status, flight performance and sexual signalling in wild-type parrots

During mate choice, individuals are predicted to assess traits that honestly signal the quality of potential partners. Locomotor capacity may be such a trait, potentially signalling condition and ability to resist oxidative damage. In this study, we experimentally manipulated nutritional status: Male wild-type budgerigars, imported from Australia, were provided with either an enhanced (EQ) or reduced quality (RQ) diet varying in vitamin (particularly retinol and α-tocopherol) and mineral levels. Then, we assessed whether this influenced locomotor capacity, i.e. escape flight performance, and sexual attractiveness in male budgerigars Melopsittacus undulatus. Males in the EQ group showed significantly greater total antioxidant capacity and higher blood plasma concentrations of the dietary antioxidants retinol and α-tocopherol, but not carotenoids, than the RQ group. Over 8 weeks of flight training, males on the EQ diet showed significantly greater improvement on the most strenuous flight test than RQ males. In mate choice trials, females preferred EQ over RQ males. EQ males that were relatively fast in escape flight trials were more strongly preferred in the mate preference arena than their RQ competitors. Interestingly, males with high plasma carotenoid levels flew slower and were less attractive than males with low carotenoid levels. This might indicate that carotenoids are not effective antioxidants in birds. Overall, our results show that dietary-derived antioxidants can influence sexual attractiveness and other fitness-related traits through multiple pathways. Locomotor capacity appears to be an honest signal of male condition in birds.