Document Type


Date of Degree Completion

Spring 2022

Degree Name

Master of Science (MS)



Committee Chair

Alison Scoville

Second Committee Member

Taza Schaming

Third Committee Member

Clay Arango


Clark’s nutcracker, a bird in the family Corvidae, is in a mutualistic relationship with an obligatory partner, whitebark pine (Pinus albicaulis), a keystone species currently declining due to infection by white pine blister rust (Cronartium ribicola), attacks from the mountain pine beetle (Dendroctonus ponderosae), a changing fire regime, and climate change. Effects from blister rust and changes to fire management strategies began strongly impacting conifers, particularly whitebark pine, in the early 1900s. Because Clark’s nutcrackers are the only efficient seed dispersers for whitebark pine, it is critical to understand their diet, movement, and caching behavior. Nutcrackers eat whitebark pine seeds, along with those of multiple other conifers, as a critical winter food source. However, no previous research has been able to compare current and historical nutcracker diet, specifically changes before and after the introduction of blister rust and fire suppression practices. Understanding nutcracker diet changes will help predict nutcracker seed dispersal behavior as whitebark pine declines. Using feather stable isotopes from museum specimens, I analyzed the relative diet, inferred from δ15N and δ13C ratios, to assess diet shifts over seasons, life stages, and years. δ15N indicates trophic changes between plant- and animal-based material, and δ13C indicates potential elevational, latitudinal, and water stress effects as well as derivation from C3 or C4 photosynthetic pathways. δ15N value shifts between seasons showed significant increases in trophic level (i.e. a diet of more insects and other animal material) during the summer and decreases in trophic level (i.e. a diet of more seeds) during the spring and fall seasons. Overall, adults consume a lower trophic level diet than juveniles, indicating a higher utilization of conifers. There was no significant change in δ15N values between 1888 and 2016, indicating the proportion of plant- to animal-based material in their diet remained consistent over time. However, δ13C values declined between 1888 and 2016, and further research is needed to help identify what changes in δ13C values mean for their conifer mutualists.

Available for download on Wednesday, August 04, 2027