Most migrating birds need to stopover in between flights in order to refuel. Lately, additional purposes of stopover have been suggested, including physiological recovery from metabolically demanding migratory flight. One apparently unavoidable, but harmful physiological effect of migratory flight is increased oxidative damage to lipids and proteins. We here, for the first time, tested whether migrating birds are able to reduce their oxidative damage during stopover. To be able to collect longitudinal data on a large number of individual birds, we temporarily caged wild northern wheatears, a long-distance migrant which does not suffer stress when caged during migration. Around noon on the first and third day at stopover, the birds were blood-sampled to determine malondialdehyde concentration, a commonly used marker of oxidative damage to lipids. We found that malondialdehyde concentrations significantly decreased during stopover, a result unchanged when correcting for the peroxidizability of the substrate. The extent of the decrease was unrelated to the amounts of food consumed or of fuel accumulated. Our findings support the hypothesis that stopovers serve reduction of oxidative damage, warranting re-thinking of how birds accomplish their migrations. They also highlight the need to include physiological recovery as a driver of the (temporal) organization of migration.

The data presented are parameters of the oxidative balance, food intake and changes in fuel stores in temporarily caged migrating northern wheatears (Oenanthe oenanthe). The oxidative balance parameters were taken on both the first and third full day in captivity. Food intake was total food intake during days 1-3. Changes in fuel stores were calculated from the first to third morning in captivity.

The sample size for antioxidant capacity is much lower because of limited plasma volumes.