Factors Influencing Diet Selection by White-Tailed Deer

Abstract

Variables characterizing the use and nutritive value of 34 spring and summer foods of whitetailed deer (Odocoileus virginianus) in the Missouri Ozarks were subjected to principal component analysis. Four factors, explaining 73.5% of the variation in the data, were extracted. Because the chemical and structural composition of spring and summer foods varied widely, selection of different forage types (forbs, fruits of woody species, leaves of woody species, grasses, and grain) satisfied different nutritional needs. Forbs and grasses had high digestibility and contained high levels of protein, phosphorus, and potassium. Leaves of woody species, although poorly digested, provided significant amounts of rapidly fermented cell solubles, had a high calcium content, and probably were rapidly passed through the digestive system. Fruits of woody species were high in energy. Habitat in nonagricultural areas of the midwest should be managed to stimulate the production of each forage type if deer carrying capacity is to be increased. J. WILDL. MANAGE. 46(3):711-718 The nutritional content of foods eaten by large generalist herbivores (e.g., ungulates, equines, lagomorphs) is highly variable (Westoby 1974, Belovsky 1978). A given food item may meet an animal's nutritional requirement for energy but be unable to meet its requirements for some other nutrient, such as calcium. Thus, the animal must select a diet from a number of food items of unequal nutritive value that provides a nutritionally adequate mix of essential nutrients. For a herbivore population that is within the carrying capacity of its range, voluntary intake, at least during the growing season, is probably limited by gut capacity and the turnover time of food in the digestive tract rather than by search time (Westoby 1974, 1978). Therefore, in terms of diet selection, the chemical and structural composition of a forage, as well as the ability of the animal to digest and metabolize it, should be more important than availability when voluntary intake is limit d by digestive capacity (Westoby 1974). Westoby (1980) has shown that consumption of a particular forage by black-tailed jack rabbits (Lepus californicus) is constrained only when availability of the forage is low. In this paper, we attempt to explain the variation in the frequency, digestibility, solubility, and chemical and structural composition of forages that comprise the spring and summer diet of white-tailed deer in the Missouri Ozarks. Populations of white-tailed deer in the Missouri Ozarks are well within the carrying capacity of their range (Korschgen et al. 1980). Therefore, the diet of these deer should represent a diet that is at least selective, if not optimal, with regard to its