White-tailed Deer are ruminants. The process of rumination (gathering a lot of food at once and then digesting it later by chewing one’s cud) is fully developed by the age of about two months, or roughly by the end of July. Fawns can be completely weaned and survive without milk at this time, but does often don’t wean them until 3 to 4 months. It’s not unheard of to see a fawn born in May or June still nursing, or attempting to, in October. It stands to reason that it’s hard to give up this valuable source of nutrition, for deer milk is richer in fat, protein and energy than cow’s milk. (Photo taken by Erin Donahue on September 2nd.)
The diet of White-tailed Deer varies with the seasons, but in general deer require a high-quality diet and tend to choose the most nutritious options available. In addition to mast (fruit, acorns, beechnuts) and browse, herbaceous plants and fungi make up the greatest portion of their food. However, their foraging choices are extensive. White-tailed Deer have been known to consume the washed-up carcasses of alewives after they (the alewives) have spawned as well as insects, mice and the nestlings of ground-nesting songbirds.
Microorganisms inside a deer’s four-chambered stomach enable cellulose in the plant material consumed to be digested. In winter, the microorganisms within the deer stomach are different from the microorganisms in spring, summer, and fall. This change allows deer to digest a diet of woody browse during winter months and turn the high-fiber diet into proteins through intricate physiological processes. Offering food items during this period other than woody browse (such as hay) is detrimental to deer, as it requires different microorganisms in the stomach in order to be digested. Thus, even though a deer’s stomach might be full (of hay, for instance), it may starve due to the inability to digest it. (Photo: shelf fungus eaten by White-tailed Deer, showing lower jaw incisor grooves)
Being ruminants, white-tailed deer have a four-chambered stomach which allows them to digest a wide variety of food, including leaves, twigs, fruits and nuts, grass, corn, alfalfa, and even lichens and fungi. Their stomach hosts a complex set of microbes – organisms such as bacteria, which are too small to be seen with the naked eye – that change as the deer’s diet changes through the seasons.
In general, the green leaves of growing plants are consumed in the spring and summer, while fruits and seeds are eaten as they become available. Hard mast foods, such as hickory nuts and acorns, are an extremely important component of fall and early winter diets when deer need to establish fat reserves. The buds and twigs of woody plants are a mainstay of their diet in winter.
At this time of year it is not unusual to see deer grazing in fields that are just starting to have a touch of green. Grass is a welcome change from their winter woody diet, but it only comprises a very small (less than 8%) of a deer’s overall diet, due to its low crude protein and digestibility. Because their rumen (the stomach chamber where most microbial fermentation takes place) is small relative to their body size, a white-tailed deer’s diet must be high in nutritive value and capable of being rapidly degraded in the rumen. Therefore, white-tailed deer rely primarily on alfalfa, clover, beans and other legumes, additional herbaceous flowering plants, and browse, all of which have more protein and are more easily digested than grasses.
Moose are ruminants, as are cattle, goats, sheep and deer; they have a four-chambered stomach, which is necessary in order to digest the cellulose in the vegetation they consume. Food goes to the rumen and the reticulum, the first two chambers, which contain bacteria and other microorganisms that help digest the cellulose as it mixes with saliva. Here the food separates into solids and liquid material and the solids clump together to form the cud, which is regurgitated and chewed a second time in order to break it down into smaller bits. The third chamber, or omasum, functions as a pump, sending the food to the final chamber, the abomasum, where the digestion process is completed.
The highlight of a recent trip to Maine was watching a bull moose feed on submerged aquatic vegetation. It would swim a short distance, and then sink, much like a submarine, until only the top of its back was visible, and then it, too, completely disappeared, leaving no sign of a moose. Seconds later the moose’s head would reappear, with its mouth full of green plants. When these plants were consumed, the moose would submerge underwater again and come up with another mouthful. It proceeded to do this at least a dozen times before eventually swimming to shore. When moose are feeding on submerged vegetation they are capable of reaching plants in water over 18 feet deep, and they can remain under water for up to 50 seconds or longer before resurfacing. It’s thought that they remain submerged by paddling and perhaps by releasing air from their lungs.
A white-tailed deer’s diet consists of a wide variety of herbaceous and woody plants, the ratio of one to the other being determined by the season. Fungi, fruits and herbaceous plants form much of the summer diet. Dried leaves and grasses, acorns, beechnuts and woody browse are important autumn and early winter food. After snowfall, the winter diet consists mostly of woody browse (twigs, leaves, shoots and buds) from many different trees (maples, birches and cedars among them). Come spring, deer eat buds, twigs and emerging leaves. Deer are ruminants (as are cattle, goats, sheep and moose). They have a four-chambered stomach, which is necessary in order to digest the cellulose in the vegetation they consume. Food goes first to the rumen, the first of the four chambers, which contains bacteria and other microorganisms that help digest the cellulose. Food is circulated from the rumen back to the deer’s mouth by the second chamber, or reticulum, and the deer ruminates (“chews its cud”). The third chamber, or omasum, functions as a pump, sending the food to the final chamber, the abomasum, where the digestion process is completed.