Evaluating Variation in Clark's Nutcracker (Nucifraga columbiana) Diet Using Feather Stable Isotopes

Author

Jasmine Ruiz, Central Washington UniversityFollow

Document Type

Thesis

Date of Degree Completion

Spring 2022

Degree Name

Master of Science (MS)

Department

Biology

Committee Chair

Alison Scoville

Second Committee Member

Taza Schaming

Third Committee Member

Clay Arango

Abstract

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.

Recommended Citation

Ruiz, Jasmine, "Evaluating Variation in Clark's Nutcracker (Nucifraga columbiana) Diet Using Feather Stable Isotopes" (2022). All Master's Theses. 1781.
https://digitalcommons.cwu.edu/etd/1781