Not just fuel: energy stores are correlated with immune function and oxidative damage in a long-distance migrant

In many animals,catabolic and anabolic periods are temporally separated.Migratory birds alternate energy expenditure during flight with energy accumulation during stopover.The size of the energy stores at stopover affects the decision to resume migration and thus the temporal organization of migration.We now provide data suggesting that it is not only the size of the energy stores per se that may influence migration scheduling,but also the physiological consequences of flying.In two subspecies of the northern wheatear Oenanthe oenanthe,a long-distance migrant,estimated energy stores at a stopover during autumn migration were positively related with both constitutive innate and acquired immune function,and negatively related with oxidative damage to lipids.In other words,migrants'physiological condition was associated with their energetic condition.Although time spent at stopover before sampling may have contributed to this relationship,our results suggest that migrants have to trade-off the depletion of energy stores during flight with incurring physiological costs.This will affect migrants'decisions when to start and when to terminate a migratory flight.The physiological costs associated with the depletion of energy stores may also help explaining why migrants often arrive at and depart from stopover sites with larger energy stores than expected.We propose that studies on the role of energy stores as drivers of the temporal organization of(avian)migration need to consider physiological condition,such as immunological and oxidative states.

Revealing the control of migratory fueling： An integrated approach combining laboratory and field studies in northern wheatears Oenanthe oenanthe

Migratory birds rely on fueling prior to migratory flights. Fueling in migrants is controlled by intrinsic as well as ex- trinsic factors. From captive studies we have started understanding the internal mechanisms controlling bird migration. Field studies have demonstrated the effects of external factors, such as food availability, weather, competitors, parasites or diseases, on the stopover behavior of migrants. However, an integrated approach is still missing to study coherently how the innate migration program interacts with the varying environmental cues and to estimate the contribution of the innate migration program and the environment to realized migration. The northern wheatear Oenanthe oenanthe offers a unique opportunity for integrated studies. It breeds across almost the whole Holarctic with just a ＂gap＂ between eastern Canada and Alaska. All breeding populations over- winter in sub-Saharan Africa which makes the northern wheatear one of the most long-distant migratory songbirds with extraor- dinary long non-stop flights across oceans. It is a nocturnal migrant which travels without parental or social aid/guidance. Thus, young birds rely entirely on endogenous mechanisms of timing, route selection and fueling on their first outbound migration. By establishing indoor housing under controlled conditions the endogenous control mechanisms of northern wheatear migration could be revealed. At the same time, environmental factors controlling fueling could be investigated in the field. On migration wheatears occur in a variety of habitats with sparse vegetation where their stopover behavior could be quantitatively studied in the light of ＂optimal migration＂ theory by the use of remote balances, radio-tagging and even experimentally manipulated food availability. The present paper summarizes our approach to understand the control of migration in northern wheatears by combin- ing field and laboratory studies at various spatial and temporal scales, and linking various sub-disciplines .

Corrigendum to: Not just fuel: energy stores are correlated with immune function and oxidative damage in a long-distance migrant

Current Zoology 2019 doi:10.1093/cz/zoz009 Advance Access Publication Date:7 March 2019.