Deer rely heavily on their diet for survival and to maintain ecological balance. Understanding their eating habits provides insight into their adaptability and their important role in natural environments. Their daily food consumption is a complex interplay of various factors.
The Daily Food Requirement
An adult deer typically consumes a substantial amount of forage each day, generally ranging from 6% to 8% of its body weight during spring through fall. This translates to approximately 4 to 9 pounds of green foliage and browse daily for an average-sized deer. This intake represents the dry matter content of the food, which is the weight of the material after all moisture has been removed.
The diet of a deer primarily consists of browse, forbs, and mast, collectively making up over 85% of their overall food intake. Browse refers to the leaves, buds, and tender shoots of woody plants like trees, shrubs, and vines. Forbs are non-woody, broad-leaved plants, and include various herbaceous species and some agricultural crops such as soybeans. Mast encompasses hard or soft fruits, including acorns, nuts, and berries. While deer are capable of eating grasses, these typically constitute a relatively small portion of their annual diet, often less than 5%.
Factors Influencing Consumption
A deer’s daily food intake fluctuates based on intrinsic and extrinsic factors. Body size and age play a significant role, with larger, growing deer generally requiring more food to support their development. Young, growing deer, for instance, need higher protein levels in their diet, ranging from 16% to 20% of their dry matter intake, compared to adults who require about 6% to 8% for maintenance. Older animals, conversely, tend to consume less per unit of body weight.
Sex and physiological state also influence consumption. Bucks, especially during the breeding season known as the rut, have increased energy demands and may lose a significant amount of body weight. Antler growth in bucks can elevate their energy requirement by up to 22%. Pregnant and lactating does have considerably higher nutritional needs to support gestation and milk production, with lactation placing the greatest protein demands on a deer. A deer’s activity level directly correlates with its caloric needs; more active individuals will require more food.
Habitat quality and availability greatly affect a deer’s diet. Areas with abundant, high-quality forage allow deer to meet their nutritional requirements more efficiently. Deer are selective feeders, choosing plants that offer the highest palatability and nutritional value. A diverse array of plant species in a habitat is beneficial, as it allows deer to select a quality diet even as nutrient levels in plants change seasonally.
Seasonal Dietary Shifts
Deer exhibit seasonal dietary shifts, adapting their consumption patterns to changing food availability and metabolic requirements. In spring and summer, when vegetation is lush and abundant, deer primarily consume fresh green foliage. This includes tender leaves, new shoots, forbs, and soft fruits, which are rich in nitrogen and easily digestible. This period is crucial for growth, fawn development, milk production in does, and rapid antler growth in bucks, leading to high daily food intake.
As autumn arrives, deer shift their focus towards building fat reserves. Their diet during this time includes calorie-dense foods such as mast (acorns and nuts) and agricultural crops like corn and soybeans. Deer increase their food intake during September and October, accumulating fat by as much as 20% to 30%. Bucks also experience high energy expenditure during the rut in autumn, further driving their need for calorie-rich foods.
Winter presents the greatest challenge due to scarce high-quality forage, colder temperatures, and snow cover. Deer rely heavily on woody browse, twigs, and buds, as well as evergreen leaves from plants like white cedar, arborvitae, and yews. To conserve energy, deer enter a state of metabolic slowdown and reduce their food intake, regardless of availability, relying on stored fat reserves for up to 40% of their daily nutritional needs. They can lose between 15% and 20% of their body weight over the winter months.