Biology of White-Tailed Deer
Deer are probably the best recognized and most widely distributed large mammals in North America. The white-tailed deer is found in nearly every state in the United States. Deer can be found throughout the southern provinces of Canada, in tropical forests of South America, or in the midst of an urban location in Michigan. Deer are creatures of the forest edge and thrive in agricultural areas interspersed with woodlots and riparian habitat. They favor forest stands in early succession where brush and sapling browse are within reach. Dense forest cover is used for winter shelter and protection.
Female does have the ability to reproduce within their first year, and does over three years usually produce twins and triplets. In addition, the health of a doe, often a function of habitat quality, influences her reproductive capacity as females from the best range produce more fawns than those from poor range.
In Michigan, the deer-mating season typically occurs during late October through December, while it peaks in November. Does are in estrus for 24 hours every 28 days. If not bred, does will cycle two or three times until bred. One buck may breed several does, and a doe may be bred by more than one buck. Gestation lasts about 200 days, and the peak of fawn drop is mid-May to mid-June. Fawns weigh seven to eight pounds at birth and are able to walk shortly thereafter. For the first couple of weeks, does leave their fawns in a hiding place for several hours at a time, returning briefly to nurse them. This strategy reduces the likelihood of predators locating the newborn fawn. Fawns begin to follow their mother on her foraging trips at about four weeks of age. White-tailed deer fawns are nursed for eight to ten weeks before they are weaned.
The diet of white-tailed deer changes with the seasons. Succulent herbaceous plants, such as ferns, wild strawberry, dandelions, and goldenrod are preferred by deer during the summer months, and these “forbs” are supplemented with berries, mushrooms, new leaves from trees, and aquatic plants. A wide variety of agricultural crops are also eagerly consumed by deer, including corn, soybeans, oats, barley, alfalfa, pumpkins, and potatoes. In the autumn, deer continue to make use of available agricultural crops but turn to hard mast crops that are high in energy, such as acorns and beechnuts, as well as soft mast such as apples and other fruits. They also consume hay and clover at this time. During winter, deer abruptly change their diet in northern areas to stems and buds of woody plants. Favorite winter “browse” species in Michigan are white cedar, maple, birch, aspen, dogwood, and sumac, as well as many shrubs.
Social Structure and Behavior
The social organization of white-tailed deer is largely matriarchal where an adult doe may be accompanied some of her female offspring from previous years, and all their fawns. Sometimes three or four generations of related does are present in a family group. When fawning season arrives in mid-May, adult does leave the family group and remain alone to bear and rear their fawns. At this time, young males may disperse from their mother’s home range. If siblings remain together throughout most of summer, yearling bucks will separate in September as the rut approaches. Yearling does remain in the mother’s home range and generally rejoin their mother and her new fawns between September and October. During the breeding season adult and yearling bucks tend to stay alone except when in pursuit of a female approaching estrus. After the breeding season, yearling and adult bucks form loose associations of small groups of anywhere from two to six animals, which remain together throughout most of the winter and summer months.
The size and shape of a deer’s home range varies with deer density, sex, landscape conditions, habitat quality, and season of the year. Deer occupying better habitats can fulfill all their necessary requirements in smaller areas whereas deer residing in poorer ranges may have to travel further distances to find suitable food and cover. Males generally have larger home ranges than females.
Male deer grow a new set of antlers each year beginning in March or April. A skin called “velvet,” which contains nerves and blood vessels that supply nutrients, covers the growing antlers. Antler growth is usually complete by late July. The velvet is shed late August or early September, often hastened by rubbing on small trees. Polished antlers are carried throughout most of the breeding season and are cast during winter (usually in late December and January) as testosterone levels decline. Male fawns grow pedicles that are typically about one inch in length. Yearling bucks tend to grow antlers having two (spikes) to eight points depending on nutrition and genetic qualities of both its mother and father. A deer may reach the maximum number of points early in life; however the mass of the antlers continue to grow, even though the number of points may not. Bucks will produce their largest antlers after reaching physical maturity at four to five years of age. Although a buck’s antlers may decline with advanced age, few bucks in Michigan live long enough to show antler size regression.