Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Dr. Christopher G. Guglielmo


Migratory birds complete amazing journeys between their breeding and wintering grounds. Each journey comprises a series of flights that last hours to days, followed by stopovers where fuel stores are replenished. Despite the long flights undertaken by migratory birds, where respiratory water losses are high for extended periods of time, birds are not dehydrated after flight. My studies demonstrate that birds maintain hydration by modulating rates of endogenous water production in response to rates of water loss. In resting, water restricted house sparrows (Passer domesticus) I used quantitative magnetic resonance body composition analysis (QMR) and hygrometry to demonstrate that stressed resting birds increase the rate of lean mass (protein) catabolism to liberate water and maintain osmotic homeostasis. I then flew Swainson’s thrushes (Catharus ustulatus) in a climatic wind tunnel under high- and low-humidity conditions for up to 5 hours. Flight under dry conditions increased the rate of lean mass loss, endogenous water production and plasma uric acid concentrations. This demonstrated that atmospheric humidity influences fuel composition in flight and suggest that protein deposition and catabolism during migration are a metabolic strategy to maintain osmotic homeostasis during flight. Next, I investigated the metabolic response to flight in the American robin (Turdus migratorius). These birds have high rates of endogenous water production early in flight due to a high contribution of carbohydrate and protein to energy during the transition to fat oxidation, and do not require additional protein catabolism to maintain water balance. Migratory birds may reduce excretory water losses to avoid dehydration in flight. I investigated kidney function in fed, rested and flown Swainson’s thrushes and found no decrease in glomerular filtration rate during flight, however they rely on increased water reabsorption to reduce excretory water losses in flight and at rest. Finally, the effect of diet on mitochondrial metabolism was investigated. I demonstrated that the performance increases often attributed to high dietary polyunsaturated fatty acids are likely due to reduced rates of production of reactive oxygen species by mitochondria. Together, these studies advance our knowledge of the metabolic response to the environment in the context of bird migration.