How Birds During Migration Maintain (Oxidative) Balance

Abstract

Animals dynamically adjust their physiology and behavior to survive in changing environments, and seasonal migration is one life stage that demonstrates these dynamic adjustments. As birds migrate between breeding and wintering areas, they incur physiological demands that challenge their antioxidant system. Migrating birds presumably respond to these oxidative challenges by up-regulating protective endogenous systems or accumulating dietary antioxidants at stopover sites, although our understanding of the pre-migration preparations and mid-migration responses of birds to such oxidative challenges is as yet incomplete. Here we review evidence from field and captive-bird studies that address the following questions: (1) Do migratory birds build antioxidant capacity as they build fat stores in preparation for long flights? (2) Is oxidative damage an inevitable consequence of oxidative challenges such as flight, and, if so, how is the extent of damage affected by factors such as the response of the antioxidant system, the level of energetic challenge, and the availability of dietary antioxidants? (3) Do migratory birds ‘recover’ from the oxidative damage accrued during long-duration flights, and, if so, does the pace of this rebalancing of oxidative status depend on the quality of the stopover site? The answer to all these questions is a qualified ‘yes’ although ecological factors (e.g., diet and habitat quality, geographic barriers to migration, and weather) affect how the antioxidant system responds. Furthermore, the pace of this dynamic physiological response remains an open question, despite its potential importance for shaping outcomes on timescales ranging from single flights to migratory journeys. In sum, the antioxidant system of birds during migration is impressively dynamic and responsive to environmental conditions, and thus provides ample opportunities to study how the physiology of migratory birds responds to a changing and challenging world.

More than mortality: Consequences of human activity on migrating birds extend beyond direct mortality

“…Introduced plants alter community structure and composition by replacing native species (McKinney 2004, Burghardt et al 2009, Nelson et al 2017) and reducing stopover habitat quality (McWilliams et al 2004, 2021; Guglielmo et al 2017). Important nutritional components in berries serve as antioxidants and immune stimulants in migrating birds (reviewed by Cooper-Mullin and McWilliams 2016), and native fruits often contain greater concentrations of energy, fat, or antioxidants than introduced ones (Bolser et al 2013, Smith et al 2013, Oguchi et al 2017, but see Cullen et al 2020).…”

Fat Stores and Antioxidant Capacity Affect Stopover Decisions in Three of Four Species of Migratory Passerines With Different Migration Strategies: An Experimental Approach

“…During short-term captivity, ad lib-fed Blackpoll Warblers and Red-eyed Vireos increased their fat stores and nonenzymatic antioxidant capacity more than individuals of the same species fed at maintenance levels, indicating that food availability on stopover allows individuals to increase nonenzymatic antioxidant capacity. Although the exact mechanism is unknown, it is likely that increased food availability on stopover leads to higher levels of non-enzymatic antioxidant capacity either directly via dietary antioxidants (DeMoranville et al, 2021;McWilliams et al, 2021) or through upregulation of endogenous antioxidants to combat an increase in RS production from lipid peroxidation . These results confirm previous work from Block Island that found fat stores were positively correlated with nonenzymatic antioxidant capacity in free-living Red-eyed Vireos and Blackpoll Warblers (Skrip et al, 2015).…”

“…However, within individual Northern Wheatears (Oenanthe oenanthe) in the spring, oxidative damage to polyunsaturated fatty acids decreased over 3 days, indicating that birds can recover from the damage incurred during a previous flight (Eikenaar et al, 2020), although the contribution of dietary antioxidants from fruits to oxidative recovery is still unclear. Thus, the ability of a bird to forage effectively for dietary antioxidants, recover from oxidative damage, and to rebuild fat and antioxidant stores on a stopover site may influence behavioral decisions (e.g., length of stay on a stopover, direction of subsequent migratory flights) that affect overall timing and success of migration (McWilliams et al, 2021), but this has not been thoroughly studied.…”

Altered dynamics of mitochondria and reactive oxygen species in the erythrocytes of migrating red-headed buntings

“…Heart enlargement ( Trivedi et al, 2014 ), hematocrit increase ( Butler, 2016 ), the liver hypofunction aiding fat mobilization from adipose tissue ( Guglielmo, 2010 ), altered muscle size dynamics with insulin-like growth factor, and IGF1 rise ( Price et al, 2011 ) are prominent physiological changes. Blood mediates the multitude of supplies such as oxygen and energy metabolites amid heightened hypoxia-reoxygenation physiology ( McWilliams et al, 2021 ).…”