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Stable isotopes of a consumer organism can be used to estimate the proportional utilization of food items that have different isotopic signals to estimate changes in diet over time.Using stable isotopes as biotracers has become a useful tool for investigating trophic dynamics in ecosystems. Recent advances in the theory of stable isotope dynamics and food web modeling have extended the utility of natural variations in stable isotope abundance. However, as a growing field, some potentially useful approaches to using stable isotopes remain untested. Here, we used stable isotopes of nitrogen (δ 15 N) and carbon (δ 13 C) to validate their utility in examining the feeding relationships of plains sharp-tailed grouse (Tympanuchus phasianellus jamesi; hereafter sharp-tailed grouse) in southern Alberta, Canada. Sharp-tailed grouse are known to consume mostly plants and opportunistically utilize insects and spiders as a high protein food source between May and October.Primary feathers obtained from hunter harvested grouse were analysed and used to estimate diet proportions of vegetation and arthropods during this time frame. Stable isotope measurements of primary feathers were able to show seasonal changes in sharp-tailed grouse diet. Our results indicated that sharp-tailed grouse may primarily utilize nutrients obtained from insect prey (mainly grasshoppers) for feather synthesis during molt, and that the isotope signals found in primary