Adult males may attain the following dimensions: total length 1040-2400 mm; length of tail 100-365 mm; length of hind foot 280-540 mm; length of ear 140-230 mm; weight 90-125 km. Females average 20-40% smaller. White-tailed Deer may live 20 years or more in captivity but seldom live longer than 10 years in the wild.
White-tailed deer are gregarious, forming both family groups and mixed foraging groups. Males are solitary during rut except when pursuing or tending estrous females. Dominance hierarchies influence behavior. The matriarch is dominant in family groups, whereas size and condition determine dominance in males. Activity is crepuscular, and white-tailed deer rarely are seen during the day. They are wary when moving to feed or to a bedding site. Bucks in rut are noteworthy for their "rubs" and scrapes that are used to establish dominance and to communicate with females. Thirteen distinguishable vocal and non-vocal sounds that are used in communication among individuals have been recognized. During spring and summer males are solitary and previous family groups disperse, but in fall and winter they may gather in small bands to browse and shelter. Where food is plentiful, white-tailed deer may concentrate and remain for some time, forming "deer yards." In other cases, when food is more dispersed, the "yarding" habit is not seen.
Rut lasts from late September through January, peaking in November. Bucks compete for individual does and build harems. As with other deer, the neck and shoulders of the males become swollen. Gestation lasts about 202 days, after which a doe bears one to two fawns (twins) depending on her age and condition, usually in May. Triplets are rare. At birth, a fawn weighs about 1.7 kg. During the first week of life, the fawn remains concealed while the doe feeds. Later it begins to follow the doe short distances, and after a month accompanies her everywhere. Weaning to solid food takes place over a period of several months, but by autumn the young are independent. Fauns frequently remain with their mothers during winter. They lose their spotted coat when the molt in August or September. Fawns may breed at 6 months of age and may produce offspring as yearlings, although litter size usually is reduced. However, most females do not breed until they are 1 1/2 half years old, which is also when males achieve sexual maturity.
Before large predators were eliminated, the principle predators on adult deer were pumas and wolves. The puma has returned to Kansas and probably preys largely on deer. However, natural predation on adults is inadequate to control deer populations, and hunting picks up some of the slack. Nevertheless, deer tend to overpopulate.
White-tailed deer are both browsers and grazers, selecting the most nutritious forage available. Grasses and forbs dominate the diet in spring and early summer, whereas succulent new-growth leaves and twigs are favored in mid-summer. In autumn fruits are important in the diet, and in winter foods consumed are determined largely by availability. Agricultural crops are an important year-round source of food.