Deer are often pictured as gentle herbivores, grazing peacefully on grass and leaves. While this perception is largely true for the bulk of their diet, it is incomplete. The simple classification of deer as strict plant-eaters does not account for their surprising adaptability. When faced with environmental pressures or specific nutritional needs, deer consume a variety of non-plant items. This dietary flexibility is a complex biological truth about survival in the animal kingdom.
The Foundation: Deer as Primary Herbivores
Deer are classified as ruminants, possessing a four-chambered stomach designed to process tough, fibrous plant material through fermentation. They are considered “concentrate selectors,” preferring highly nutritious and easily digestible plant parts over coarse grasses, unlike true grazers such as cattle. Their digestive system is optimized to select forbs, which are broad-leafed herbaceous plants, and the tender new growth of woody plants.
The majority of a deer’s caloric intake comes from this selective plant diet, which varies significantly with the seasons. During spring and summer, deer consume protein-rich forbs, succulent leaves, and the soft tips of branches, known as browse. In colder months, their diet shifts to evergreen browse, dormant buds, and hard mast like acorns and beechnuts, which provide concentrated energy for winter survival.
As browsers, deer rely heavily on shrubs, twigs, and tree leaves, allowing them to access food even when deep snow covers ground-level vegetation. Their smaller mouths and specialized digestive tracts enable them to efficiently pick out the most palatable and nutrient-dense plant species. This plant-based foundation sustains their rapid growth, high metabolism, and reproductive needs throughout the year.
The Surprising Reality of Non-Plant Consumption
Despite their classification, deer are opportunistic omnivores, occasionally consuming animal matter. One commonly observed deviation is osteophagy, the practice of gnawing on animal bones, shed antlers, or even turtle shells. Studies have recorded deer engaging in this behavior to extract hard-to-find minerals.
Instances of deer consuming meat are rare but documented, often involving scavenging rather than active hunting. They have been witnessed eating dead fish, consuming the remains of small mammals, and even scavenging the guts of other deer left by predators or hunters. These acts demonstrate a willingness to exploit any available energy source.
Perhaps most surprisingly, deer have been observed preying on the nests of ground-nesting birds, consuming both eggs and nestlings. This behavior is usually noticed in early spring when plant growth is minimal and high-protein food sources are scarce. The consumption of animal products, including insects and carrion, confirms their dietary flexibility.
Nutritional Drivers for Omnivory
These occasional instances of consuming animal matter are driven by specific biological requirements that their plant diet sometimes fails to meet. The main motivation for gnawing on bones and antlers is a deficiency in macrominerals, particularly calcium and phosphorus. These minerals are necessary for skeletal health, antler growth in bucks, and milk production in pregnant or lactating does.
During late winter and early spring, available plant matter often contains lower concentrations of these vital nutrients. Consuming bone provides a highly concentrated and readily available source of calcium and phosphorus, superior to what can be obtained from woody browse. This behavior is a survival mechanism to balance their internal chemistry.
The consumption of eggs, nestlings, and carrion is a response to a temporary need for high-quality protein and fats, especially during periods of nutritional stress. A doe nursing fawns or a buck growing new antlers has elevated protein demands that are difficult to satisfy solely with low-quality winter forage. By opportunistically consuming animal matter, deer maximize their chances of survival and reproductive success.