1. Physiological processes, including those that disrupt oxidative balance, have been proposed as key to understanding fundamental life history trade-offs. Yet examination of changes in oxidative balance within wild animals across time, space and major life history challenges remain uncommon. For example, migration presents substantial physiological challenges for individuals, and data on migratory individuals would provide crucial context for exposing the importance of relationships between oxidative balance and fitness outcomes. 2. Here we examined the consistency of commonly used measures of oxidative balance in longitudinally sampled free-living individuals of a long-lived, long-distance migrant, the Brent goose Branta bernicla hrota over periods of months to years. 3. Although inter-individual and temporal variation in measures of oxidative balance were substantial, we found high consistency in measures of lipid peroxidation and circulating non-enzymatic antioxidants in longitudinally sampled individuals. This suggests the potential for the existence of individual oxidative phenotypes. 4. Given intra-individual consistency, we then examined how these physiological measures relate to survival and reproductive success across all sampled individuals. Surprisingly, lower survival was predicted for individuals with lower levels of damage, with no measured physiological metric associated with reproductive success. 5. Our results demonstrate that snapshot measurements of a consistent measure of oxidative balance can inform our understanding of differences in a key demographic trait. However, the positive relationship between oxidative damage and survival emphasises the need to investigate relationships between the oxidative system and fitness outcomes in other species undergoing similar physiologically challenging lifecycles. This would highlight the extent to which variation in such traits and resource allocation trade-offs is a result of adaptation to different life history strategies. 30-Mar-2020

Live capture of wild brent geese using cannon nets on wintering and staging grounds.

Blood sampling from tarsal vein - each sample centrifuged and flash frozen in the field. Samples maintained at -80 prior to analysis.

Aliquots of plasma assayed for malondialdehyde, super oxide dismutase, total antioxidant and uric acid concenrations.

Many birds do not have all four of the oxidative stress assays

Birds do not always have a current or subsequent associate status (single/pair/family) if this could not be accurately assigned in the field