Background/Question/Methods Foraging by white-tailed deer (Odocoileus virginianus) populations that are at high densities can have deleterious effects on forest growth and regeneration. It remains unclear if white-tailed foraging efforts are targeted towards highly favored tree species, or if they forage without displaying preference among tree species. According to optimal foraging theory, white-tailed deer should select tree species that possess the greatest nutritional constituents (e.g. crude protein, sugars, starches), while they will avoid ingesting trees that possess large quantities of anti-nutritional compounds (e.g. tannins and other polyphenols). Optimal foraging by deer may lead to decreased forest diversity and function by suppressing proliferation of preferred species. The objective of this study was to discern if deer forage preferentially on trees of the greatest benefit. We conducted a cafeteria-style preference study, in which we presented semi-tame deer with a choice of eight different deciduous and coniferous trees to forage on. We identified preference by discerning the total number of bites taken from each tree in a 24 h period, and then compared preferences to the nutritional and anti-nutritional composition of each tree species. Tree constituents that we analyzed were crude protein, non-structural carbohydrates, tannin, and total polyphenols. Results/Conclusions We found that deer selected for deciduous trees species over coniferous trees. Deciduous trees in our study contained a higher percentage of crude protein than the coniferous trees did. However, species such as American elm (Ulmus americanus) had a crude protein content consistent with many of the avoided, coniferous tree species, yet American elm were still more highly preferred. Trees that possessed little or no tannin were more highly preferred than trees with higher tannin concentrations. We also found that deer would forage upon, and in some instances prefer, tree species with a high tannin concentration when the tree also possessed a high percent of crude protein. We suspect that this is due to the tannin-binding salivary compounds that white-tailed deer possess, which enable them to counteract the costs imposed by tannins. We suspect that volatile organic compounds (VOCs), which are known to be emitted by coniferous trees, may have negatively influenced deer preference. We shall incorporate VOC emissions into our study so that we may elucidate the type of VOCs that deer avoid. We will use this information on tree species that deer will avoid as a food source when calculating carrying capacities for white-tailed deer.
