White-tailed deer are ungulates, or hoofed mammals, belonging to the family Cervidae. Characteristics distinguishing this group from other hoofed mammals are forked antlers, a four-part stomach and the absence of a gall bladder. The whitetail is the only remaining native ungulate still thriving in Missouri. Ancestors of our modern deer actually had five toes. Through evolution the first toe disappeared, the second and fifth toes became dew claws, and the third and fourth toes enlarged to form hooves. As a result, deer actually walk on their toes or, more precisely, on their toenails. Like our fingernails and toenails, hooves are composed of keratin. As whitetails grow older, their hooves become wider. Experienced trackers can tell yearling deer from adults based on this characteristic.
A whitetail's coat and color tend to change throughout the year. During the summer months, deer are reddish-brown, and their coats are rather thin-less than a quarter-inch thick. By August or September they shed their summer pelage, or coat, and replace it with a thick, brown-grey winter coat sometimes more than 1-inch thick. The winter pelage is made up of both a short underfur and outside guard hairs. This dense layer of hair may weigh up to 2.8 pounds. The molt/shed cycle begins again in April when deer start to grow their summer coats. This almost continual shedding and regrowth requires substantial amounts of protein and energy.
Occasionally, deer have either all white, very dark brown or piebald coats. White deer are usually albinos. This genetic trait is sometimes prevalent in one area, but it is not common anywhere. Deer that have patches of both white and brown hair are called piebald deer. These animals may have a patchwork as extensive as that of a pinto horse, or it may be less pronounced. Dark brown or black, albino and piebald deer are legal game in Missouri.
Whitetails have four sets of external glands that are used primarily for communication (Figure 2). Gland secretions can describe a deer's social status, breeding condition and health. The most recognized glands are the tarsal and metatarsal glands, located on a deer's hind leg. The tarsal gland, located on the leg's inner surface, serves to identify individuals. The metatarsal gland, found lower on the leg and on the outside, may help in regulating the animal's body temperature. Interdigital glands, located between the hooves, probably leave scent trails for other deer to follow. Pre-orbital glands function as tear glands and may relay sex and social hierarchy when rubbed on branches.
Figure 2. Whitetails have four sets of external glands that are used primarily for communication. Gland secretions can describe a deer's social status, breeding condition and health.
Antlers and Antler Growth
Whitetails are probably best known and sought after for their antlers. Sometimes incorrectly referred to as horns, deer antlers are cast and regrown annually. Horns, on the other hand, grow continually much like hooves. Another difference between horns and antlers is that horns, like hooves, are composed of keratin, whereas antlers are composed of bone. The actual composition of antlers depends upon their stage of growth. Growing antlers are 80 percent protein and 20 percent ash. Hardened antlers are roughly 63 percent ash, 22 percent calcium, 11 percent phosphorus and 4 percent organic matter. Antlers are most dense on young deer and tend to become more porous as the animals grow older.
The phrase, "the head grows according to the pasture," is probably more accurate when stated, "the body grows according to the pasture." Antler growth requires a substantial amount of protein and minerals, yet body growth always takes precedence. This is true especially for young deer because they are still putting energy into body growth.
Measuring specific nutritional and mineral effects on wild deer antler growth is difficult because of the animals' large home range and varied diet. A number of studies on penned deer have found relationships between nutrition and antler growth in young deer. Whitetail fawns fed a ration containing less than 9.5 percent protein developed smaller racks, weighed less and cast their antlers earlier than fawns fed 16 percent protein rations.
Although spring nutrition is important for body and antler growth, whitetails possess adaptations that enable them to prosper in areas with mineral deficiencies. For example, deer deposit minerals in their skeletons throughout the year. Then, during antler growth, they mobilize these minerals to the growing antlers. A second adaptation is their ability to change absorption rates of minerals in their stomach. When using large amounts of minerals for antler growth, deer siphon more minerals from their diet. Deer rely on plants for these minerals, and they select plants offering the highest mineral concentrations.
Protein and minerals play an important role in deer growth and antler development. Yet under normal weather conditions in decent habitat, deer are able grow to their potential without supplementation. A recent study that took place in an area with markedly poor soils found no significant difference between body weight or antler size in two populations of wild deer. One group had unlimited access to mineral blocks, and the other did not. In another study, deer with access to food plots were not heavier nor did they have larger antlers than deer without access to food plots.
The large number of big deer and racks that come from north Missouri, however, suggests the abundance of agricultural plantings seems to influence deer body size and antler growth. Nutrition is important, but other factors, such as genetics and age, probably play a role in the antler growth of deer in Missouri. Most studies that examine the effects of genetics on antler growth are studies of penned deer. Whether these findings may be extrapolated to wild populations remains in question. One theory suggests that spike bucks-bucks, usually yearlings, with non-branched antlers-are genetically inferior. Another has found that many of these spike bucks are late-born fawns whose antler development is retarded but will eventually catch up with other bucks.
No doubt if we take 100 bucks and feed them the same rations until they reach 4 1/2 years of age, antler development will vary among these deer. Much of this variance probably is caused by genetics. Genes and nutrition aside, however, a 3- to 7-year-old deer in Missouri will have a "braggin' sized" rack because Missouri has good deer habitat. Most deer never reach their potential because they are harvested the first year they grow antlers.
In the spring, whitetails seek out protein-rich foods, which promote growth spurts and weight gain.
The Four Stomachs
Whitetails, like most herbivores, are ruminants. This means they have a four-part stomach (Figure 3) and, like cattle, regurgitate food from their first stomach to "chew the cud," which aids the digestive process. As ruminants, deer can use many foods indigestible to humans and other nonruminants. A deer's stomach contains microbes that break down cellulose-the fibrous parts of plants-and ferment carbohydrates, thus providing energy and nutrients. This process is especially important for animals living on low-quality forage.
Rumen: This largest stomach compartment lies on top of the intestines. It functions both as a storage and fermentation chamber. Food is mixed with bacteria and protozoa, which aid the digestive process. When a deer feeds, it quickly fills its rumen. Later, it regurgitates the food and chews it more thoroughly. Rechewing helps digestion and allows microbes to break down cellulose and other plant fibers into easily digested materials.
Reticulum: This compartment lies forward of the rumen. It forces water into the rumen, suspending food particles and floating them to the reticulum where the digeston continues. Similar processes occur in the rumen and reticulum, but most material in the reticulum consists of smaller particles. Food also passes to the esophagus for rechewing.
Omasum: For the most part, the function of the omasum is to absorb water and minerals produced through digestion and to move food to the last stomach compartment, the abomasum.
Abomasum: This compartment most closely resembles the stomach of nonruminants. It secretes enzymes that further digest the products created by microbial action and the microbes themselves. Further digestion takes place in the small intestine.
Deer Weights and Growth Patterns
Generally deer from northern climates have larger body sizes and weigh more than their southern counterparts. This principle, called Bergman's Rule, holds true for most mammals and is most pronounced at the extreme northern and southern reaches of an animal's range. Animals with larger body sizes have a proportionally smaller body surface to keep warm during cold weather. Smaller body sizes are more efficient at cooling during hot weather.
Deer weights also may vary by region within a state (Table 1). In Missouri, deer are heavier and sport better racks in the northern half of the state. Latitude may play a role, but the range quality likely plays a greater role. Superior soils and abundant agriculture in northern Missouri offer better nutrition. The largest recorded deer taken in Missouri weighed 407 (live weight) pounds and was killed in 1979 in Davies County.
Deer lose weight during winter and then undergo a phase of rapid growth during spring. Bucks often lose weight during the breeding season, but regain it during spring. Females with fawns begin to lose weight in January and do not regain it until late summer when fawns are weaned. Some studies suggest deer undergo stress periods and lose weight during hot dry periods.
| Average Dressed Carcass Weights (lbs) | ||||||
|---|---|---|---|---|---|---|
| Female | Male | |||||
| Region | Fawns | Yearlings | Adults | Fawns | Yearlings | Adults |
| Glaciated Plains | 67.6 | 100.7 | 111.7 | 72.1 | 123.5 | 154.8 |
| Osage Plains | 48.0 | 77.9 | 84.7 | 54.0 | 93.9 | 128.2 |
| Ozark Border | 51.7 | 84.8 | 92.6 | 58.2 | 101.0 | 132.7 |
| Ozarks | 47.0 | 76.9 | 86.5 | 53.2 | 86.7 | 125.2 |
Activity Patterns and Home Range
Most deer activity takes place around dusk and dawn with brief
periods of activity during midday. These patterns vary with the
time of year and the weather. Recent studies suggest that deer
are most active at low humidities and show increased movement
during overcast periods. High winds decrease deer movements, and
approaching storms increase them. During winter, deer move later
in the morning and increase activity during warm spells.
Deer activity varies by season with peaks during spring and fall. The least active months are January, February and June through August. During fall, deer are active during breeding periods and while feeding to prepare for winter. Spring brings abundant food resources, and deer have increased metabolic demands due to pregnancy and growing antlers. Females are more active than males from January to July, and males are more active from September to October. Buck fawns are more active than doe fawns. Road kill data collected by the Missouri Department of Conservation and the Missouri Highway and Transportation Department show kill rates are highest during fall with smaller peaks during spring (Figure 4).
The size and shape of a deer's home range vary with habitat quality, deer density, sex, time of year and the deer's age. Deer that live in the best habitats can satisfy all their daily requirements in a smaller area; deer that live in less diverse habitats must travel to find suitable food and cover. Most home ranges tend to be elongated, and researchers theorize that this shape maximizes available resources. Deer living in diverse habitats with lots of edge and an even distribution of food and cover tend to have more circular home ranges. Adult bucks have larger overall home ranges than does and young bucks. As a general rule, deer have the smallest home ranges during summer and the largest during fall.
