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Extramural Research

Grantee Research Project Results

Grantee Research Project Results

Application of Stable Isotopes (δ13C and δ15N) to Explore the Effects of Forage Enhancement on White-Tailed Deer Foraging Selectivity and Population Density

EPA Grant Number: F07F71131
Title: Application of Stable Isotopes (δ13C and δ15N) to Explore the Effects of Forage Enhancement on White-Tailed Deer Foraging Selectivity and Population Density
Investigators: Darr, Ryan L.
Institution: Texas A & M University
EPA Project Officer: Zambrana, Jose
Project Period: September 1, 2007 through September 1, 2009
RFA: GRO Fellowships for Graduate Environmental Study (2007)
Research Category: Academic Fellowships , Ecological Assessment , Fellowship - Range and Wildlife Management



Greater population densities and foraging selectivity among white-tailed deer can lead to severe browsing of higher quality vegetation, causing a shift in community structure toward less palatable and less diverse vegetation. Contemporary human actions often lead to forage enhancement, the direct or indirect provision of a dietary supplement to wildlife, which may increase deer selectivity and density. The objective of my study, therefore, is to explore the effects of forage enhancement on white-tailed deer foraging selectivity and population density and to assess the possible environmental impact.


I will use carbon (δ13C) and nitrogen (δ15N) stable isotope tracers to reconstruct diets with a 2-source isotopic mixing model. Research will occur in South Texas where enhanced forages, in the form of pelleted supplemental feed, are commonly provided to deer. For the selectivity study, I plan to use tame deer and a bite count technique to compare the nutritional quality of plants consumed to the amount of supplemental feed in the diet. I will assess female body condition and fetus numbers in the spring plus review fall density estimates to explore the effects of supplemental feed on deer density. This will also allow me to explain feed dependency patterns in locations with different deer densities.

Expected Results:

I expect to find that deer will become more selective when supplemental feed is available. However, selectivity and the potential for environmental harm should vary depending on the quantity of feed consumed by an individual deer. For the density study, I anticipate results showing that females consuming more supplemental feed will exhibit a greater body condition and fawn:doe ratio, suggesting that they will successfully recruit more fawns into the population. I also expect to find that deer with access to supplemental feed will be sustained at higher densities and that deer will consume more feed in locations with higher deer densities.

Supplemental Keywords:

δ13C, δ15N, Forage Enhancement, Forage Quality, Foraging Selectivity, Herbivory, Nutrition, Population Density, Productivity, Stable Isotope, Vegetation Community, White-tailed Deer,

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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