Oxidative damage to lipids is rapidly reduced during migratory stopovers

Abstract

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. Abstract 1. 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.2. 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 (MDA) concentration, a commonly used marker of oxidative damage to lipids.3. We found that MDA 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. 4. 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. K E Y W O R D Savian, eco-physiology, migrant, optimal migration, oxidative stress

Urban ecophysiology: beyond costs, stress and biomarkers

“…Within-individual changes can reveal important information about the range and capacity of responses across time and contexts. Although oxidative damage is not directly a physiological response, but an outcome, it was recently shown that even oxidative damage to lipids can vary rapidly within an individual (Eikenaar et al, 2020). Thus, it would be highly valuable to also view oxidative damage as a variable trait, and to explore patterns of clearance and regeneration of oxidative damage over time to establish when it actually becomes a threat to fitness.…”

A quasi-experimental approach using telemetry to assess migration-strategy-specific differences in the decision-making processes at stopover

“…Relating detailed knowledge of the birds' intrinsic condition, e.g. energy stores [7], age [65,66], sex [67], migratory destination [21], physiology [5,6] and immune system [68], to the departure decision may eventually allow formulating distinct conditions at which "most" individuals decide to resume migration or to remain at stopover. Such an approach neglects the migratory history of the birds before they entered the stopover site and their future expectations of better or worse conditions elsewhere [48,69] which differ between individuals.…”

“…This could be a signal in the decision-making process to remain at this more favourable stopover [41], as the exploitation of higher energy accumulation rates than before would be tantamount to an increase in the migration speed [48,49,56]. Alternatively, these long-staying redstarts might need longer to physiologically recover from the previous energetically demanding migratory flight than the others [5]. Regarding the potential influence of the weather on the departure decision, temperature, air pressure, precipitation and wind conditions (Additional file 1: Figure S1) did not deteriorate during the 5 days after the day of capture (Additional file 1).…”

“…While travelling between breeding areas and wintering grounds, migrant birds alternate their flight bouts with periods of rest, so-called stopovers. Since actively flying during the endurance airborne periods is energetically and physiologically extremely demanding [ 1 – 3 ], birds sleep [ 4 ], recover [ 5 , 6 ] and fuel [ 7 ] during a stopover. If birds have recovered and prepared for the next upcoming migratory flight, and if environmental conditions are favourable, these intrinsic and extrinsic conditions signal the decision-making processes of the innate migration program to continue migration [ 8 – 10 ].…”

Changes in fat mass affect the motivation to migrate in northern wheatears

“…Many individual migrants, however, do not arrive at stopover with fully depleted fuel stores, and fuelling is not the only reason why migrants land at a stopover site. Migrants may land, for example, to avoid flying during the day (Alerstam 2009) or in inclement weather (Shamoun-Baranes et al 2017), to reduce the amount of oxidative damage incurred during flying (Eikenaar et al 2020), or because they need to compensate for sleep loss as a consequence of nocturnal flight (Ferretti et al 2019). For those migrants carrying enough fuel to support the next flight, the effect that fuel stores may exert on the motivation to depart from stopover may not be as clear cut as it is for lean individuals.…”