Using stable isotope analysis to explore the exploitation of anthropogenic foods by Sciurus carolinensis and Tamias striatus at varying levels of availability

Date of Award


Document Type

Restricted (Opt-Out)



First Advisor

Kathleen LoGiudice




small mammal, gray squirrel, eastern chipmunk, stable isotope analysis, anthropogenic food, urban-rural gradient


Urban and suburban areas are continuing to grow and spread into natural habitats causing wildlife to face more anthropogenic pressures. Habitat fragmentation is also increasing which typically results in decreased species richness and viability in a given area, but some studies show that species with generalist diets may take advantage of urban ecosystems by exploiting anthropogenic food sources. To explore this idea, I conducted live trapping of eastern chipmunks (Tamias striatus) and gray squirrels (Sciurus carolinensis) at various levels of anthropogenic food availability to obtain a fur sample and conduct stable isotope analysis. Stable isotope values δ13C and δ15N reflect the long term diet of an organism throughout its molting period due to isotopic fractionation that occurs in plants and the accumulation of animal protein through trophic levels. Eastern chipmunks were captured on Union College campus, residential properties, and rural forests while gray squirrels were captured on Union College campus and a rural deciduous forest. Anthropogenic food availability is highest on campus due to open trash cans and dumpsters, intermediate on residential properties, and lowest in rural forests. Isotopic signatures of gray squirrels from urban locations were significantly higher in δ15N and δ13C than their rural counterparts (p<0.0001, p<0.003, for δ15N and δ13C, respectively; t-test). Eastern chipmunks followed a similar pattern such that the isotopic signatures of chipmunks from urban sites were significantly higher in both δ15N and δ13C in comparison to their rural equivalents (p<0.0001, p<0.004; t-test). This suggests that the animals are exploiting anthropogenic food sources when available. Further analysis of the chipmunk data revealed differences within site types. Signatures of eastern chipmunks from residential properties with bird feeders were significantly higher in δ13C than those without feeders and rural sites (p<0.007, Tukey HSD), likely a reflection of corn that is often present in bird seed. Isotopic signatures of eastern chipmunks from the Albany Pine Bush at a site dominated by nitrogen fixing black locust (Robinia pseudoacacia) trees were significantly lower in δ15N than any other location (p<0.0001, Tukey HSD). Overall, the exploitation of anthropogenic foods by small mammals is reflected in the isotopic signatures of their fur, but underlying factors such as local vegetation may disrupt these patterns

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