Season, anthocyanin supplementation, and flight training have mixed effects on the antioxidant system of migratory European starlings (Sturnus vulgaris)

Migratory birds engage in two periods of endurance flight annually as they travel between summer breeding and overwintering grounds, and such endurance flights likely incur oxidative costs. These costs may differ between fall and spring migration, especially for females who must prepare for breeding and egg laying in spring. The objective of this study of a migratory bird was to test proposed hypotheses about how key components of the female's antioxidant system differ in response to flight training in the fall and spring and to dietary antioxidant supplementation. We hand-raised female European starlings (Sturnus vulgaris) and then fed them either a diet supplemented with dietary anthocyanins or a diet without added anthocyanins. We then flew females in a windtunnel for 15 days during fall and spring migration seasons and measured over time oxidative damage (d-ROMs) and three components of the antioxidant system—non-enzymatic antioxidant capacity (OXY), uric acid, and glutathione peroxidase (GPx) activity. Prior to flight training, non-enzymatic antioxidant capacity and oxidative damage were lower in females during spring compared to fall, and females fed a low-antioxidant diet had consistently higher circulating uric acid. GPx activity decreased more in spring immediately after a long-duration flight. Females fed a high-antioxidant diet had a greater decrease in non-enzymatic antioxidant capacity after the 15-day flight training. Flight-trained females had higher circulating uric acid than untrained females immediately after the longest-duration flight, and decreased GPx activity after the 15-day flight training. In sum, females upregulated enzymatic and non-enzymatic endogenous antioxidants in spring, and females fed a diet with less antioxidants appear to compensate by increasing circulating uric acid. Our findings emphasize the important role of dietary antioxidants for birds during migration, and that similar flights in fall and spring likely represent distinct oxidative challenges in the life history of female birds.