Deer are herbivores with a diverse diet that adapts to their environment and the changing seasons. Their feeding habits are driven by nutritional needs and the availability of various plant types. Understanding what deer naturally consume and how this changes seasonally is important for appreciating their ecological role and ensuring their welfare.
Natural Foraging Habits
Deer primarily consume a variety of plant matter, relying on four main categories: browse, forbs, mast, and grasses. Their four-chambered stomach allows them to efficiently process fibrous foods and extract nutrients from a wide range of vegetation.
Browse refers to the leaves, twigs, and buds of woody plants like trees, shrubs, and vines. Examples include honeysuckle, greenbrier, and young maple or oak shoots. This category forms a significant portion of a deer’s diet, especially when other food sources are scarce. Deer typically select the youngest, most tender growth for higher digestibility.
Forbs are non-woody, broad-leaved herbaceous plants, often referred to as “weeds.” These include plants such as ragweed, clover, and wild strawberry. They are highly digestible and rich in energy, minerals, and protein. Forbs are particularly important in late spring and summer, providing essential nutrients for deer growth and antler development.
Mast encompasses the fruits and nuts produced by trees and shrubs. This includes soft mast like berries (e.g., blackberries, grapes, plums) and apples, and hard mast such as acorns, chestnuts, and beechnuts. Mast provides concentrated sources of carbohydrates and fats, important for energy storage, especially before colder months. Deer actively seek these high-energy foods when they ripen.
Grasses are generally a less preferred food source for deer compared to browse and forbs. Deer typically eat grasses when young and tender, such as early-stage cereal grains. Their digestive system is better adapted to digesting broad-leaved plants than the high-fiber content of mature grasses.
Seasonal and Regional Dietary Shifts
A deer’s diet is dynamic, shifting significantly with the seasons and varying across different geographical regions due to changes in food availability and nutritional demands. These adaptations allow deer to thrive in diverse environments.
In spring, deer focus on new, succulent growth. They heavily consume abundant forbs, which provide high levels of protein and energy for recovery from winter, antler growth in males, and lactation in females. Grasses may also be eaten during their early, tender stages.
Summer brings abundant plant life. Deer continue to seek protein-rich forbs and the leaves and shoots of woody browse. Soft mast, such as berries, begins to ripen, offering an additional energy source. During this period, deer consume a large volume of green foliage and browse daily to maintain health and support growth.
Fall is a time for deer to build fat reserves for winter. Their diet shifts to prioritize mast crops, particularly hard mast like acorns and chestnuts, which are rich in fats and carbohydrates. Agricultural crops, if available, such as corn and soybeans, also become important sources of concentrated energy. This consumption helps them store energy for the rut and winter.
During winter, when many plant sources are dormant or snow-covered, deer primarily rely on woody browse. This includes twigs, buds, and bark from shrubs and young trees like honeysuckle, maple, and sometimes evergreens like cedar. Their metabolism slows, and they utilize fat reserves accumulated in the fall to survive. Digestive microorganisms adapt to process these high-fiber, low-quality foods.
Regional differences in flora dictate specific dietary components. For instance, deer in areas with abundant oak forests consume more acorns, while those in agricultural landscapes may incorporate more crops. The availability of specific browse species, forbs, and mast varies by ecosystem, leading to localized dietary preferences.
Foods to Never Offer Deer
Providing human-sourced foods to deer can have negative consequences for their health and behavior. Despite good intentions, many common human foods are harmful. These effects range from digestive problems to increased disease transmission and changes in natural behavior.
Corn is a dangerous food to offer deer, especially in large quantities or during winter. Deer are ruminants, and their digestive system contains specialized microbes that adapt to seasonal forage. A sudden influx of high-carbohydrate foods like corn can disrupt this microbial balance, leading to acidosis or “grain overload.” This causes a rapid drop in stomach pH, killing beneficial bacteria and impairing digestion, which can result in bloating, diarrhea, dehydration, and even death within days.
Bread, pastries, and other processed human foods are similarly problematic due to their high carbohydrate content and lack of appropriate nutrients. These items can cause the same digestive distress as corn, as deer’s systems are not equipped to handle refined starches. Even apples, while natural in small amounts, can contribute to acidosis if consumed in large quantities, particularly when deer are accustomed to a high-fiber winter diet.
Hay, particularly in winter, can also be detrimental. While deer may eat it, their gut microbes might not be prepared to digest dried grasses if they haven’t gradually adapted. Deer have been known to starve with stomachs full of hay because they cannot extract nutrients. Pet food, formulated for different digestive systems, is inappropriate and can lead to nutritional imbalances or digestive upset.
Beyond digestive issues, artificial feeding concentrates deer in smaller areas. This increases the risk of disease transmission, such as Chronic Wasting Disease (CWD) and other parasites. Feeding can also make deer dependent on human handouts, altering their natural foraging behaviors and making them less wary of humans, which can lead to increased conflicts and vehicle collisions.