The white-tailed deer is a widespread mammal across North America, often observed foraging in open areas or near human development. This visible behavior frequently leads to the assumption that grasses, like those found in pastures or lawns, constitute a major part of their diet. Deer are actually biologically adapted to consume a different type of forage, which is why they are only occasionally seen grazing on turf. This article explores the biological reasons for the deer’s selective diet and the specific circumstances under which they consume grasses and other plants.
Deer Diet: Browsers Versus Grazers
Deer are classified primarily as browsers, preferring to eat leaves, twigs, buds, and fruits from woody plants and shrubs. This dietary preference contrasts sharply with grazers, such as cattle or sheep, which subsist mainly on high-fiber grasses. The difference between these feeding types lies in the anatomy of the deer’s digestive system.
The white-tailed deer is a concentrate selector, meaning its relatively small, four-chambered stomach requires highly digestible, nutrient-dense food sources. This system is adapted for a quick passage rate, maximizing the intake of easily metabolized plant contents like starch, protein, and fat. Mature grasses are high in cellulose fiber, which demands a slow digestive turnover rate to break down effectively. Therefore, their digestive biology drives them toward low-fiber forbs and woody browse.
Specific Grasses and Forbs Consumed
The preferred low-lying plants deer consume are forbs, which are broad-leaved herbaceous plants often known as weeds. These forbs are typically lower in fiber and significantly higher in digestible protein than grasses. Legumes, such as alfalfa and various species of clover, are sought after because their crude protein content can easily exceed 16%, providing the energy required for antler growth and lactation.
Deer do consume certain grasses, but these are generally restricted to the tender, young growth of cool-season varieties. New sprouts of fescue, rye, or wheat are palatable because they have not yet developed the tough, lignified cell walls of mature blades. These young shoots contain a higher concentration of simple carbohydrates and protein, mimicking the nutrient profile of preferred forbs.
Agricultural fields are frequently targeted because young crops, including winter wheat, oats, and soybeans, offer an easily accessible, high-energy food source. Native forbs such as beggar’s lice, ragweed, and pokeweed are also highly preferred, with some species offering crude protein levels well over 20% during the growing season.
Seasonal Changes in Forage
The deer’s consumption of grasses and forbs is heavily influenced by seasonal nutritional pressures. Forage quality is highest during the spring green-up when young shoots emerge, providing a flush of highly digestible feed. This early protein boost is important for does preparing for fawning and males beginning antler growth.
During the summer and fall, the diet shifts toward woody browse, leaves, and mast, such as acorns and berries. These items offer high energy and are lower in fiber than maturing grasses. Mature, warm-season grasses become coarse and fibrous, causing deer to abandon them for energy-rich alternatives.
Grass consumption often becomes an emergency measure during severe winter scarcity, especially when deep snow covers preferred woody browse. Although mature, frozen grass provides minimal nutritional value, deer will consume it to fill their rumens and maintain digestive activity. Their primary winter diet consists of the buds and twigs of woody shrubs and trees, browsed when better forage is unavailable.
Protecting Lawns and Gardens
Physical Barriers
Preventing deer damage often requires installing physical barriers. A permanent woven-wire fence must be at least eight feet tall to deter a motivated deer from jumping over it. A less visually intrusive alternative is a specialized double fence, consisting of two parallel four-foot fences spaced four feet apart, which confuses the deer’s depth perception.
Electric Fences
Low-voltage electric fences offer a cost-effective behavioral deterrent. These are often baited with a peanut butter mixture on foil flags to attract the deer, conditioning them to avoid the area after a mild shock. This method is most effective when deer have alternative food sources and are not under pressure to feed.
Chemical Deterrents
Chemical deterrents can be applied, typically working through either scent or taste. Scent-based repellents, often containing putrefied eggs or blood meal, mimic the smell of predators or decay, but they require frequent reapplication, particularly after rain. Taste-based products use hot or bitter ingredients to make the plant unpalatable, training the deer to avoid certain species.
Adjusting Planting Choices
Adjusting planting choices is an effective long-term strategy for minimizing damage to landscaping. Deer generally avoid plants with strong aromatic oils, fuzzy textures, or those that are known to be toxic. Examples of less palatable ornamentals include lavender, sage, and foxglove, which are often passed over for more succulent garden plants.