Dietary n-3 Long-Chain Polyunsaturated Fatty Acids Alter the Thermoregulatory Phenotype of a Migratory Shorebird

AbstractMigrating birds balance high energy expenditure required in flight with extended bouts of feeding at stopover to refuel, and strategies that permit birds to conserve energy during migration could benefit their overall performance. Energy conservation through reduced body temperature permits animals to save energy, similar to controlled heterothermy (i.e., torpor). Furthermore, dietary n-3 long-chain polyunsaturated fatty acids have been hypothesized to prime flight muscles to improve migration performance, although this has not been tested in a thermoregulatory framework. Here, we test how the energetic and thermoregulatory performance of western sandpipers (Calidris mauri) is influenced by dietary n-3 long-chain polyunsaturated fatty acids. Dietary fatty acid manipulations did not affect basal, resting, or summit metabolic rate in response to cold. Birds also had a similar body temperature at rest over 24 h regardless of diet. However, sandpipers fed a diet high in n-3 long-chain polyunsaturated fatty acids had lower body temperature after a response to cold ($5.98\pm 1.80$ [SE]), and lower body temperature was associated with reduced metabolic rates at low temperatures in comparison to birds fed a high-monounsaturated fatty acid diet. These results indicate that n-3 long-chain polyunsaturated fatty acids change the thermoregulatory phenotype of western sandpipers but without consistent changes in energetics using standard measurements. Our findings suggest that ecological variation in the availability of different dietary fatty acids could affect thermoregulation in shorebirds. Increasing sea surface temperatures may reduce the availability of n-3 long-chain polyunsaturated fatty acids, making it important to understand their role in the physiology and performance of animals that consume them in high abundance.