Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Master of Science




Hobson, Keith A.


Using stable isotope measurements of inert tissues to determine origins and migratory patterns is well established. However, isotopically determining nutritional origins of lipids, the primary fuel of migration, has not been attempted. I explored isotopic links between diet and stored lipids in captive White-throated Sparrows (Zonotrichia albicollis) and true armyworm moths (Mythimna unipuncta) using δ13C and δ2H measurements. Isotopic discrimination between body lipids and diet was established as linear calibration functions. Isotopic uptake following a diet switch in moths was used to trace lipid accumulation over time. Isotopic correlations between breath metabolic by-products of fed and fasted sparrows were explored as indicators of lipid use. This study established isotopic (δ13C, δ2H) linkages between diet and stored lipids for migratory insects and passerines and advocates the use stable isotopes in lipids as a tool to evaluate nutrient origins and allocation strategies in a variety of migratory species.

Summary for Lay Audience

Migration is a phenomenon that occurs across a large variety of species and is key to the survival of many organisms. The primary fuel for migration in most organisms is lipids but determining where these lipids are synthesized, how they are used, and how they are replenished is difficult using traditional means. Tracking migration has benefited from using intrinsic markers such as naturally occurring stable isotopes. Isotopes are forms of the same element with different kinetic properties due to differences in atomic mass. These isotopes differ across the natural environment due to a variety of biogeochemical processes and are integrated into animal tissues, such as feathers or claws, often in fixed and traceable patterns. Though lipids contain primarily carbon and hydrogen, the traceability of lipids through isotopes of these elements for the purposes of tracking nutritional strategies in migratory organisms has not been explored. My study investigated the isotopic relationship between diet and body lipids using stable hydrogen and carbon isotopes in two model organisms, the White-throated Sparrow and the true armyworm moth. By providing the study organisms with diets that were grouped via a 2x2 experimental design with combinations of high 13C, low 13C, high 2H, and low 2H, I investigated if different diets would lead to differential isotopic values in lipids synthesized from the diet. Carbon and hydrogen isotopic values of the lipids corresponded strongly with the diet from which they were made. Additionally, isotopic dietary changes performed on the moths were reflected in the uptake and storage of lipids over time. When sparrows were fasted and induced to burn lipids, the breath CO2 and water vapour arising from lipid metabolism also reflected isotopic distinctions of the diet treatments. In conclusion, isotopic connections between diet and stored lipids for migratory insects and sparrows were established. This study advocates the use isotopic measurements of lipids as a tool to evaluate nutrient origins and allocation strategies in a variety of migratory species.