Deer are a common sight in many landscapes, from wild forests to suburban backyards. Their presence often sparks curiosity about their eating habits, particularly if they graze like livestock. Understanding their diet provides insight into their role in ecosystems and their interactions with human environments.
Do Deer Graze?
While deer can consume grass, it is not their primary or preferred food source. Grazing refers to animals like cows or horses feeding on low-growing grasses, which their digestive systems are well-suited to break down. Deer are not primarily grazers and cannot survive solely on mature grass due to its low nutritional value and their limited ability to digest it.
Deer will eat young, tender grasses, particularly in early growth stages, and may consume it more frequently in suburban areas or when other food sources are scarce. Grass constitutes a small percentage of their overall diet, often as little as nine percent. Their digestive system is not designed to efficiently extract nutrients from large quantities of fibrous grass, unlike primary grazers.
The Broader Deer Diet
Deer are primarily browsers, consuming leaves, twigs, buds, and bark from woody plants and other vegetation. This contrasts with grazing, as browsing involves eating plants typically off the ground. Their diet is diverse and adaptable, with deer eating over 400 plant species in some regions.
Beyond woody browse, their diet includes forbs—broad-leaved herbaceous plants like clover and ragweed—that offer high protein and digestible energy. They also consume hard mast like acorns and other nuts, rich in fats and carbohydrates, and soft mast like berries and fruits. Seasonal availability influences their food choices, with their diet shifting to the most nutritious options throughout the year, such as fresh vegetation in summer and energy-rich mast in fall.
How Deer Forage and Process Food
Deer are ruminants, with a four-chambered stomach that processes a diverse diet. The largest chamber, the rumen, acts as a fermentation vat where microorganisms break down plant material. Deer quickly consume food, chewing just enough to swallow, filling their rumen for later digestion.
After initial consumption, deer find a secure place to “chew their cud” or ruminate. This involves regurgitating partially digested food from the rumen back into their mouth for thorough chewing, further breaking down plant fibers. The food then passes through the other stomach chambers—the reticulum, omasum, and abomasum—for digestion and nutrient absorption before moving to the intestines. This specialized digestive process allows deer to extract nutrients from a variety of plants, including those with higher fiber content.
Ecological Impact of Deer Foraging
The foraging habits of deer influence their environment, impacting natural ecosystems and human-modified landscapes. Deer can shape plant communities by selectively consuming certain species, leading to a reduction in native plant diversity and abundance. For instance, they prefer native plants over some unpalatable invasive species, inadvertently promoting their spread.
Their browsing affects forest regeneration by consuming tree seedlings and saplings, potentially altering forest composition. This can lead to a decline in economically or ecologically important tree species like oaks and maples, while allowing less preferred species like birch and beech to become more abundant. In human-modified areas, deer consume garden plants, agricultural crops, and ornamental landscaping, leading to economic losses and conflicts. High deer population densities can exacerbate these impacts, transforming forest understories and reducing biodiversity.