Dietary antioxidants attenuate the endocrine stress response during long-duration flight of a migratory bird

Abstract

Glucocorticoids (GCs) are metabolic hormones that promote catabolic processes, which release stored energy and support high metabolic demands such as during prolonged flights of migrating birds. Dietary antioxidants (e.g. anthocyanins) support metabolism by quenching excess reactive oxygen species produced during aerobic metabolism and also by activating specific metabolic pathways. For example, similar to GCs' function, anthocyanins promote the release of stored energy, although the extent of complementarity between GCs and dietary antioxidants is not well known. If anthocyanins complement GCs functions, birds consuming anthocyanin-rich food can be expected to limit the secretion of GCs when coping with a metabolically challenging activity, avoiding the exposure to potential hormonal detrimental effects. We tested this hypothesis in European starlings ( Sturnus vulgaris ) flying in a wind tunnel. We compared levels of corticosterone, the main avian GC, immediately after a sustained flight and at rest for birds that were fed diets with or without an anthocyanin supplement. As predicted, we found (i) higher corticosterone after flight than at rest in both diet groups and (ii) anthocyanin-supplemented birds had less elevated corticosterone after flight than unsupplemented control birds. This provides novel evidence that dietary antioxidants attenuate the activation of the HPA axis (i.e. increased secretion of corticosterone) during long-duration flight.

The energy savings-oxidative cost trade-off for migratory birds during endurance flight

“…Migratory distances for this population vary from many hundreds of kilometers to several thousand kilometers, with some individuals overwintering in the Euro-Mediterranean region and others in northwest Africa ( Bairlein, 2014 ). European starlings are also quite social and curious, and quickly learn to successfully fly together in a given windtunnel as demonstrated by several recent studies ( Carter et al, 2020 ; Casagrande et al, 2020 ). We conducted two complimentary experiments that involved feeding starlings over many months two diets that differed only in the relative amounts of mono- and polyunsaturated fats ( Table 1 ), specifically the amounts of omega-9 18:1 and omega-6 (18:2) and omega-3 (18:3) (no.…”

Flight and Dietary Antioxidants Influence Antioxidant Expression and Activity in a Migratory Bird

“…Considered together, birds consuming dietary anthocyanins appear to gain protective benefits in response to immunological and exercise-related challenges, both of which are directly relevant to birds during migration. Furthermore, dietary anthocyanins reduced the production of corticosterone (CORT) in flying songbirds ( Casagrande et al. 2020 ) indicating that antioxidant consumption protects against the metabolic costs associated with high glucocorticoid levels, like reactive species production.…”

“…We propose that flight-trained birds consuming anthocyanins may have been able to upregulate antioxidant genes CAT and SOD1 in addition to metabolic genes ( DeMoranville et al. 2020 ) because these birds incurred an energy saving, perhaps through the reduction of the glucocorticoid CORT ( Casagrande et al. 2020 ).…”

“…We used European Starlings ( Sturnus vulgaris ) as representative songbirds for this study because they are abundant in the New World and Old World, they are omnivorous and acclimate well to captivity and new diets, and they have been successfully trained and flown in wind tunnels in other studies ( Hall et al. 2014 ; Casagrande et al. 2020 ).…”

How Birds During Migration Maintain (Oxidative) Balance

“…In contrast, other components of non-enzymatic antioxidant capacity as measured with the OXY test usually decrease after flight, and the extent of this acute change in OXY after flight depends on the acute response of enzymatic antioxidants such as GPx when regular daily flying is prolonged (Cooper-Mullin et al, 2019). Consumption of dietary antioxidants by European Starlings affects the response of enzymatic antioxidants as well as non-enzymatic antioxidants (DeMoranville et al, 2021;Frawley et al, 2021) and has a multitude of related effects: antioxidant consumption reduces corticosterone production in flight-trained birds, and thus potentially protects against the costs of high glucocorticoids (Casagrande et al, 2020), and enhances the breeding condition of males (Carbeck et al, 2018). The role of corticosterone during preparation for migration, in departure during migration (e.g., from stopover sites), and in support of sustained migratory flights has been recently reviewed by Bauer and Watts (2021).…”