Biology
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-gray 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 3 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, dark brown to black 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. The rarest color variation is black or melanistic. It is caused by an excess of a dark pigment called melanin. Dark brown or black, albino and piebald deer are legal game in Missouri.
Whitetails have as many as seven glands that are used primarily for communication. 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 and their social status. The metatarsal gland, found lower on the leg and on the outside, may help in advertising that there is danger in an area but its function, if any, is unclear. Interdigital glands, located between the hooves, probably leave scent trails that may express dominance. Pre-orbital glands function as tear glands and may relay sex and social hierarchy when rubbed on branches. Forehead glands likely are the source of scent left on rubs and overhanging branches that serves in communication during the breeding season. Preputial glands located inside the penal sheath have recently been discovered and also may serve in deer communication.
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, energy 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 to grow to their potential without supplementation. A 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.
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 contends 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 ½ 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.
Deer weights
Regions of Missouri
Deer weights tend to vary by region within a state. In Missouri, on average 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.
| 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 |
Note: Due to lack of good habitat, few deer were harvested from the Mississippi Lowlands Region during the dressed weight study.
The seasons
Spring
Spring is the time of plenty for deer. New succulent plants send out tender shoots. Food is abundant even in areas that do not normally provide deer with nutritious food. At this time of year, the woods become a huge salad bar, and deer are able to sample different flowers and plants as they choose. Among the spring favorites in Missouri are wild lettuce, grape vines, trumpet vine, cinquefoil, sweet clover, violets and spring beauty. Most plants offer peak nutrition during spring, and whitetails respond with growth spurts and weight gain. Males channel energy to their antlers and regain the weight lost during last year’s breeding activities. Females transfer energy to unborn fawns, which now undergo rapid growth.
Almost all Missouri does 1½ years old or older breed and produce fawns each year. In addition, 30 to 40 percent of fawns that are less than ½ year old breed and produce offspring by the time they are 1 year old. The number of fawns that are born and survive annually is dependant upon a number of factors including the age and nutrition of the mother, deer density in the area and winter stress. Birthrates vary from region to region as these factors change.
The pregnancy rate of whitetails in Missouri was measured by examining the number of fetuses in road-killed does. Pregnancy rates for deer 2½ years old and older were nearly equal, but rates for younger deer were markedly lower. Adults had moreoffspring per doe than yearlings, who had more than the youngest group. In Missouri, most adult and yearling does have twins each year. The folk tale that old does tend to be barren is a myth. Researchers documented fetuses in does over 15 years of age. In fact, some researchers suggest that older does are more successful mothers because they are experienced and have the best territories.
Peak fawning takes place in late May and June and begins when pregnant does isolate themselves and drive other deer from their fawning areas. Adult deer use the same areas each year. The establishment of fawning territories is thought to limit social stress and help distribute populations evenly. Territories also may prevent newborn fawns from imprinting on deer other than their mothers.
The first weeks of life for newborn fawns are precarious. Young fawns are vulnerable to a variety of predators, diseases, parasites and human-caused mortality. In Missouri, the major natural predators are coyotes, dogs and bobcats. To reduce exposure to predators, fawns spend most of their time bedded and hidden in heavy cover, such as hay fields, grown pastures and old fields. Studies using radio transmitters suggest fawns are active less than one-fifth of a 24-hour day. Both the doe and its offspring spend most of their time in a 10- to 20-acre area these first weeks. Does visit their fawns two to four times a day to nurse and groom them. Fawns move to a new bed site after each feeding and grooming session, but siblings generally do not bed together. During this time, does sometimes physically defend their offspring from predators. It is also during this period that people find what they believe are “abandoned” fawns. In most cases, its mother is close by. Bedded fawns should be left alone.
Following its first month, the fawn increases nursing and activity periods. After four to six weeks, a doe may visit her fawn as often as five or six times per day. Fawns begin eating vegetation and ruminating at two weeks, although they cannot digest plant nutrients until five weeks. Fawns become more social, are more likely to be seen with their siblings or mother and increase their activity to levels similar to adult does. After 10 weeks, fawns eat grasses and forbs and are functional ruminants.
Young does typically establish fawning territories next to their mother’s, but sometimes they disperse and establish in a new area. Missouri deer studies suggest does travel widely during spring then, before giving birth, reduce their movements dramatically. It is much more common for 1-year-old bucks to disperse. In a northern Missouri study that used radio transmitters, 77 percent of buck fawns roamed more than 8 miles. Dispersal by young bucks and does is especially pronounced in areas with high deer densities. Dispersing deer tend to have higher mortality rates, but they may be more likely to find vacant good habitat. This dispersal also might reduce the amount of inbreeding.
Summer
During summer, does and bucks are segregated, sedentary and spend most of their active time eating. Does and fawns travel and feed together throughout the summer. Sometimes fawns from the previous year travel with this year’s doe/fawn groups. Does with fawns may spend 70 percent of their time eating to meet their high nutritional requirements. They often seek shrubby, thick cover because it offers better hiding and higher quality forage.
Bucks often congregate in bachelor groups composed of neighboring bucks. Males typically use open habitats, such as mature hardwoods, fields and poorly stocked forests. Thus, they often are found in different habitats than family groups of does and fawns. Some deer researchers suggest males prefer open areas so they can keep track of their position in the social hierarchy and to keep from damaging their antlers while feeding. Others theorize that the males’ nutritional requirements are lower per pound of body weight or that their large rumens allow them to consume more food and gather sufficient nutrition from poorer ranges.
Activity levels in deer are proportional to their nutritional needs. Larger bucks are reported to be more active than smaller bucks during summer. Females are more active than males. Nonetheless, both sexes tend to have smaller home ranges during summer and use wooded cover during daytime periods and open areas at night.
Fall and Winter
Fall is a frenzied time of year for whitetails. Does and fawns continue to travel in groups, but now fawns aretotally weaned and does feed aggressively to recover from the stresses associated with raising them. During fall, deer eat items rich in starch and carbohydrates. In oakhickory forests, this means acorns and soft mast, such as persimmons. Deer also graze on cool season grasses and legumes, which are undergoing a resurgence of growth with cooler fall temperatures and rain.
Yearling bucks that have not dispersed the previous spring may do so in fall. According to studies, this group represents less than 20 percent of yearling bucks in Missouri. Adult and yearling buck bachelor groups break up, and bucks begin to shed their antler velvet and rub trees. An increased production of testosterone, triggered by decreasing day length, brings on the changes in buck behavior and the hardening of antlers. Rutting behavior and activity varies with the age and experience of the bucks and the sex and age ratios of the local deer herd.
Sparring matches are common prior to the break up of bachelor groups, especially among younger animals. Yearling (1½-year-old) and 2½-year-old bucks spar to size each other up without injuring themselves. Older bucks with previously established dominance tend not to participate in much pre-rut sparring.
About the time bucks decrease their sparring activities, they increase antler rubbing. Most rubs are thought to be signposts made by bucks to advertise their presence. Rubs provide visual cues and scents that inform other deer about the rub maker. Although no one knows for sure, these rubs probably relay information about social status. The number of rubs a deer makes seems to vary among individuals, but studies of penned deer have shown that adults rub more often than yearlings.
The pattern and frequency of buck sign in an area often reflect the age structure and sex ratios of the resident deer herd. Areas with mature adult bucks have more buck sign, and these areas show signs of rubbing and scraping activities earlier than areas with predominantly yearling bucks.
Scrapes also are signposts made by bucks. They probably are used to attract or keep track of breeding females and to advertise the presence of the maker. When making a scrape, a deer paws the ground and urinates on the disturbed soil. Most scrapes are made near deer travel routes under low tree branches that typically are nibbled on and marked with a scent gland from the deer’s forehead. Adult bucks make about twice as many scrapes as yearlings. Although not common,buck fawns and does have been observed freshening scrapes.
As the rut progresses, bucks become driven to find estrous does—those that are ready to breed. The period just prior to peak breeding probably offers bow hunters the best hunting of the season because bucks constantly move and search for does in heat. Rutting bucks spend more time searching for and tending to does than eating during breeding season and sometimes lose considerable weight. Bucks typically visit the various doe family units in their home range checking for estrous does.
Prior to breeding, does also increase activity levels, thus increasing the likelihood of finding a buck and being bred. Does allow a buck to breed only during the 24-hour-period when they are in peak estrous. Does that are not bred cycle again about 28 days later and may be bred in subsequent cycles. In Missouri, most adult does are bred the second and third weeks of November. Doe fawns are bred about a month later because they cycle later than adults.
Although a buck that is at least 2½ years old will generally do more breeding than a yearling buck that is 1½ years old, recent evidence suggests that even in a lightly hunted population, yearling bucks breed some of the does. The proportion of does bred by yearling bucks could be considerable in heavily hunted areas. Also, multiple paternity, where twin or triplet fawns produced by a doe have different fathers, is fairly common, ranging from 20 to 25 percent, according to studies.
Biologists have voiced concerns that not all does are bred in populations with heavily exploited bucks. This is not the case for yearling and adult does in Missouri. During a Conservation Department reproductive study, more than 90 percent of examined does were pregnant, and most breeding occurred over a fairly short time period.
During the whitetail’s courtship, bucks trail and chase does to test their receptivity to breeding. Does aid this process by urinating frequently, which allows trailing bucks to determine their stage of estrous by smelling and tasting the urine. When a buck finds a receptive doe, he remains close by, and the two mate several times. Using radio telemetry during deer studies in north Missouri, researchers determined that mating pairs sometimes spent more than 12 hours together.
As breeding activities wind down, testosterone production decreases in males, and they, in turn, begin to shed their antlers. Some studies suggest that antler shedding also is tied to nutrition because deer living on better ranges tend to carry antlers longer than those on poorer ranges. Young deer typically shed antlers earlier than adults. The older deer, who are actively breeding, shed their antlers after there are no longer does coming into estrous.
During the rut, bucks are struck by vehicles more frequently than at other times of the year and are more vulnerable to hunting. The rut leaves most bucks in poor physical condition. Besides weight losses of up to 20 percent, bucks also may suffer from battle scars and exhaustion. They often enter winter in poorer condition than the rest of the herd.
Winter can be a very difficult time of year for deer, especially in the northern states. Cold weather and reduced food availability force deer to change their habits to conserve energy and survive. Although Missouri winters are not severe, our whitetails display some of the same behaviors as their northern counterparts. These northern deer spend the winter in a sheltered area, then return to their summer range the following spring. A number of radio-tagged deer in Missouri made movements of up to 10 miles each winter then moved back to their summer ranges each spring.
Extended family members often reunite during winter. Most family units winter in the same areas each year, but deer concentrate in new areas if food is abundant. Typically, bucks and does are still segregated. Does and their offspring from several generations often form large groups while males reunite with members of their bachelor group or travel alone.
Deer reduce activity during the winter months. Studies have documented activity changes of up to 50 percent. One study found deer were active 68 percent of the time in October but only 37 percent of the time in February. Their metabolic rate slows down as their activity rate declines, and they require less energy.
During the winter months, deer readily eat foods that are rich in carbohydrates, such as acorns and waste grain. Deer also browse on young trees and shrubs— staple foods for deer in areas lacking agricultural crops and a supplement for all deer during the winter months. The degree to which deer browse certain shrub and tree species sometimes is used as an indicator of deer population levels and winter severity. Somespecies of sumac and dogwood, for example, are readily consumed by deer. Red cedar and hickory are considered starvation foods and are only eaten when populations are high.
Diet
Because whitetails are ruminants, they eat a wide variety of foods. Their four-part compound stomach enables them to break down woody browse and herbage, but they cannot digest low-quality forage, such as grass, as efficiently as cattle.
Deer are selective feeders and seek out preferred plant species. Deer have been documented eating more than 600 different types of plants. Deer in the Ozark region of Missouri live in chiefly wooded areas and rely on natural forage, such as grape vines, green briar, Virginia creeper, oak leaves, pussy toes, clovers and prickly lettuce. During spring and summer, deer eat perennial plants more than annuals.
Studies in agricultural areas of Missouri, Iowa and Ohio indicate cultivated crops comprised 41 percent, 56 percent and 48 percent respectively of deer diet by volume. Most researchers found wild browse, fruits and seeds also are major food items. Deer prefer corn, soybeans and hay from the variety of agricultural crops. Oak mast and leaves, corralberry and various forbs are important wild browse food for deer in agricultural areas. These differences in plant use and regional food habit studies are likely a reflection of plant availability. Agricultural crops may be preferred when they are available, but deer still rely on early successional plants and oak mast. Ask your local conservation agent or private land conservationist for details on which species to plant or encourage to attract deer to your land.
