The importance of antioxidants for avian fruit selection during autumn migration

All vertebrates must contend with an increase in oxidative stress during intense exercise. Birds, in particular, may be exposed to increased oxidative stress during long-distance migration, and dietary antioxidants are likely important in alleviating the deleterious effects associated with such a stressor. We evaluated whether fruit selection by birds at a migratory stopover site in southern New England was related to the antioxidant and macronutrient content of fruits from seven commonly consumed fall-fruiting shrub species. Our objectives were to: (1) quantify, for the first time, total hydrophilic and lipophilic antioxidants, as well as two types of lipophilic antioxidants (i.e., carotenoids, and tocopherols) in wild fruits consumed by migrating birds, (2) test the hypothesis that antioxidant content of wild fruits is related to macronutrient composition, and (3) relate patterns of avian frugivory to antioxidant availability and macronutrient content of wild fruits during autumn migration. We found significant differences between fruits in total lipophilic antioxidants, carotenoids, and tocopherols, but not total hydrophilic antioxidants. Viburnum spp. and Myrica pennsylvanica had the most lipophilic antioxidants and tocopherols, whereas Celastrus orbiculatus and Rosa multiflora contained the most carotenoids. Carotenoid content was positively correlated with protein content but no significant relationships were evident between the other antioxidants and macronutrients. Fruit consumption was negatively correlated with carotenoid content and was not related to any other antioxidant measure. Interestingly, the most consumed fruit species, arrowwood, was among the highest in fat, total lipophilic antioxidants, and tocopherols. These data indicate that antioxidant content differs significantly between fruit species and suggest that (1) birds can acquire different types of antioxidants depending on the fruits they select and (2) lipophilic antioxidants, especially tocopherols, may be important antioxidants for birds during autumn migration.