Deer are adaptable herbivores, consuming a wide array of plant materials found in their varied habitats. Deer are selective feeders, often choosing plants that provide the most nutritional benefit to support their growth and energy needs.
Core Natural Forage
Deer primarily consume browse, which includes the leaves, twigs, and buds of woody plants like trees, shrubs, and vines. Browse serves as a consistent food source, remaining available even when other vegetation is scarce. It makes up a significant portion of their annual diet, often around 46%. Forbs, which are herbaceous, non-woody plants, are highly digestible and rich in nutrients, making them a preferred food during periods of abundance. These plants can constitute about 24% of a deer’s diet.
Mast refers to the nuts, acorns, and fruits produced by trees and shrubs, such as oak acorns, chestnuts, berries, and apples. Hard mast, like acorns, provides high energy, fat, and carbohydrates, while soft mast, such as berries, offers sugars and vitamins. Mast is particularly important for building fat reserves due to its dense caloric content. Fungi also contribute to a deer’s diet, offering protein, carbohydrates, and minerals throughout the year.
Deer are classified as “concentrate selectors” because their digestive system is adapted to process high-quality, easily digestible forage. Their narrow snouts and long tongues allow them to precisely select specific plant parts. This enables them to extract the most nutritious components from their environment. While grasses are not a primary food source for deer, they may consume them, though grasses make up less than 10% of their annual diet.
Seasonal Dietary Changes
A deer’s nutritional needs and available food sources shift with the changing seasons. In spring, deer recover from winter and pregnant does prepare for fawning, requiring a diet rich in protein for lactation and fetal development. Emerging forbs are particularly important during this time, offering highly digestible nutrients. Bucks also begin antler growth, which demands significant protein, calcium, and phosphorus.
During summer, deer continue to seek high-protein foods to support rapid antler development in bucks and the growth of fawns. Soft mast, such as grapes and berries, becomes available and provides energy and carbohydrates. Forbs are also heavily consumed due to their high protein content. Fawns, initially reliant on their mother’s milk, begin to nibble on vegetation within a few weeks and gradually transition to solid foods.
As autumn arrives, deer focus on building fat reserves in preparation for the colder months and the breeding season. Hard mast becomes a primary part of their diet, providing dense energy. Deer increase their food intake to accumulate 20-30% more fat. In winter, food becomes scarcer, and deer reduce their food intake, relying on stored fat for up to 40% of their daily nutritional needs. They primarily consume woody browse, which is often the only food available.
Diet Across Diverse Environments
Deer exhibit adaptability, modifying their diet based on the specific food sources available in their habitat. In dense forest environments, their diet primarily consists of native browse, forbs, and mast from forest trees. They seek out a variety of woody plants and herbaceous growth that naturally occur in these areas.
Deer living near agricultural fields incorporate cultivated crops into their diet. These crops can provide highly nutritious and palatable food sources. In suburban and urban areas, deer forage on various plants. While these areas offer abundant food, they can also lead to conflicts with human residents.
The specific plant species consumed by deer vary by geographical region, even if the general categories of food remain consistent. This dietary flexibility allows deer to sustain themselves across a wide range of ecosystems, from arid climates to lush woodlands.
Foods to Avoid Feeding Deer
Feeding deer human foods or certain agricultural products can cause harm. Corn can disrupt a deer’s digestive system, leading to a condition called acidosis. This occurs because deer stomachs are not designed to process large amounts of carbohydrates, which can result in severe diarrhea, dehydration, and potentially death.
Bread is another problematic food, as it offers minimal nutritional value and is difficult for deer to digest. Consuming too much bread can lead to a buildup of lactic acid in their bloodstream, and deer may effectively starve even with full stomachs because they are not receiving necessary nutrients. Similarly, human processed foods, pet food, and hay lack the proper balance of nutrients for deer and can cause digestive issues or lead to starvation.
Certain ornamental plants can also be toxic to deer. Artificial feeding practices can also lead to unintended negative consequences for deer populations. It can cause deer to congregate in unnaturally high densities, increasing the risk of disease transmission and making them more vulnerable to predation. Additionally, deer can become habituated to human presence, leading to increased vehicle collisions and disruptions to their natural foraging behaviors.