Abstract
Migrating birds perform extraordinary endurance flights, up to 200 h non-stop, at a very high metabolic rate and while fasting. Such an intense and prolonged physical activity is normally associated with an increased production of reactive oxygen and nitrogen species (RONS) and thus increased risk of oxidative stress. However, up to now it was unknown whether endurance flight evokes oxidative stress. We measured a marker of oxidative damage (protein carbonyls, PCs) and a marker of enzymatic antioxidant capacity (glutathione peroxidase, GPx) in the European robin (Erithacus rubecula), a nocturnal migrant, on its way to the non-breeding grounds. Both markers were significantly higher in European robins caught out of their nocturnal flight than in conspecifics caught during the day while resting. Independently of time of day, both markers showed higher concentrations in individuals with reduced flight muscles. Adults had higher GPx concentrations than first-year birds on their first migration. These results show for the first time that free-flying migrants experience oxidative stress during endurance flight and up-regulate one component of antioxidant capacity. We discuss that avoiding oxidative stress may be an overlooked factor shaping bird migration strategies, e.g. by disfavouring long non-stop flights and an extensive catabolism of the flight muscles.
Highlights
Endurance flight of migratory birds is an extraordinary physical performance carried out at a very high metabolic rate which is about twice the maximum rate of exercising small mammals [1,2]
protein carbonyls (PCs) in European robins during their nocturnal migratory flight were on average higher and showed a higher variance than during the day when resting and feeding
This study is, to our knowledge, the first to measure a marker of oxidative damage and of antioxidant capacity in birds caught out of migratory endurance flight
Summary
Endurance flight of migratory birds is an extraordinary physical performance carried out at a very high metabolic rate which is about twice the maximum rate of exercising small mammals [1,2]. This high metabolic rate is maintained during non-stop flights of up to 200 h in certain species and while fasting [3]. Several particular physiological adaptations have been found which apparently enable migratory birds to perform such an extraordinary endurance exercise They include special mechanisms of lipid supply from adipose tissue to the mitochondria of the flight muscles, and a very high oxidative capacity of the flight muscles to catabolize lipids (reviewed in [2]). It appears that migratory birds have evolved ways to overcome limitations applying to mammals regarding overall metabolic rate, lipid catabolism, protein sparing and duration of endurance exercise
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