Energy expenditure during flight implicated in regulating OXY depletion but not d-ROMs
Rate of energy expended during the flight (kJ/min) was not related to levels of plasma oxidative damage (R2=0.12, Table S3; Fig. 3A) but was related to the decrease in non-enzymatic antioxidant capacity during the acute flight (R2= 0.39, Table S1; Fig. 3B). Only a quarter of birds experienced increased d-ROM levels during an acute flight suggesting that most birds employed a successful antioxidant strategy to avoid the accumulation of d-ROMs at all energy expenditures (Fig. 3A, note direction of arrow; S1C, note labels indicating d-ROM levels). Energy consumption during the flight did not explain AF levels of d-ROMs or the change in plasma d-ROMs during the flight (AF-PF; Fig. 3A, Table S3; AF: T46 = -2.018, P = 0.050, Δ During Flight d-ROMs: T46 = -1.485, P = 0.149). In contrast, OXY was lowest in birds that consumed more energy during flight (Table S3; AF: T46 = -3.133, P = 0.003), and Δ During Flight OXY decreased to the greatest extent in birds expending more energy (Fig. 3B, Table S3; Δ During Flight OXY: T46= -2.821, P = 0.007). This relationship was primarily driven by 7 individuals that decreased OXY by an average of -128 mmol l−1 of HClO neutralized (Fig. 3B and Fig. S1C), well below the mean decrease (-22.7 ± 10.4 mmol l−1 of HClO neutralized). These birds expended energy in the upper 50% range (>0.51 kJ/min was consumed by the upper 50% of individuals) (Fig. 3B and Fig. S1C), although other individuals that expended similar amounts of energy during flight did not have such extreme decreases in OXY. Instead, 5 of these birds increased uric acid by an average of 1.4 mmol, well above the mean increase (0.5 ± 0.06 mmol); whereas the remaining birds did not change these circulating measures (OXY, uric acid) from the averages.