Migratory birds are amazingly adapted for long-distance flights and can switch the fuels they rely on to support their endurance activities. Unlike humans that burn mainly carbohydrates for endurance exercise, avian flight is fueled mainly by fats and some proteins. In a recent study published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology researchers examined how white-throated sparrows (Zonotrichia albicollis) prepared for migration.
By altering the photoperiod recently captured birds were exposed to, the researchers were able to mimic winter (short days) and spring/migratory (long days) conditions. Not surprisingly, birds preparing for migration packed on extra fat stores and increased the activity of enzymes responsible for burning fats. Fats provide more energy than burning carbohydrates or proteins, so it makes sense that birds would use them for migration. As mentioned above, migratory birds are also known to breakdown organs as well as flight muscle proteins for energy. It is thought that protein breakdown may provide the birds with a metabolic source of water generated through metabolism of proteins. In fact, burning proteins creates six times more water than utilizing fats. In this way, the birds may be able to prevent dehydration during long-distance flights.
Surprisingly, these birds did not increase their lean mass even though the activity of enzymes responsible for breaking down proteins increased. These findings show that migratory birds are able to adapt their metabolism during migration to not only utilize fats but also proteins as a source of water.
CR Elowe, AR Gerson. Migratory disposition alters lean mass dynamics and protein metabolism in migratory white-throated sparrows (Zonotrichia albicollis). American Journal of Physiology – Regulatory, Integrative and Comparative Physiology.323(1): R98-R109, 2022. https://doi.org/10.1152/ajpregu.00295.2021