The Wapiti is a gregarious species with strong herding behavior. Herds tend to be larger in winter than in summer. Some herds in Kansas in the mid-1800s were said to number over a thousand individuals. In late spring, the large winter herds break up, and cows go off individually or in small groups to give birth at traditional calving grounds. Bulls remain in small herds at that time. As summer progresses, the cows, their calves, and sometimes immature bulls form larger herds of 20 to 40 individuals, but the mature bulls remain apart, either singly or in groups of 2 to about 6 animals until the reproductive season begins. Elk graze mostly after dawn and near dusk with brief intervals of grazing and resting during the day. Herds often use the same bedding ground and follow frequently-used trails. Shelter at night may be in timber, creek bottoms, or or wherever else cover can be found from cold winter winds. During spring and summer, elk often wallow in melting snow or mud.
The elk is both a grazer and browser. Grasses and forbs predominate in the diet during the growing season, whereas browse constitutes more than half of the winter diet. Being a ruminant, the wapiti "chews its cud" while at rest during the day, a process more properly called rumination.
In autumn, profound changes occur among wapiti. With the approach of rut, usually in September, mature bulls begin bugling. Elk are said to "bugle" because their call begins with a low pitch and swoops up to high, bugle-like notes, the last of which are often prolonged. These may be followed by low grunts. Similar calls may be emitted by females at times other than rut. With the onset of the rut, the bull''s neck and shoulders swell. Bulls assemble harems of as many as 30 cows, and they defend their harems against challenges from bachelor bulls. Breeding occurs from September through October. During this period, there is much challenging and threat display among mature bulls but little actual fighting among bulls. When fighting actually occurs, it may take the form of striking out with the forefeet or sparring and shoving with the antlers. By the end of October, reproduction is completed and bulls resume their solitary ways. Gestation lasts 8 1/2 months, with most calves (usually one calf per bred cow) being born in late May or early June. Newborn calves remain hidden and immobile for the first several days, and are visited by their mothers several times a day to nurse. After a few days, calves become more active and begin to follow the cow. At a few weeks of age they may begin to eat a little vegetation, but suckling continues to provide their principal nourishment throughout the summer. Weaning is a gradual process, but by autumn the calf is able to subsist on solid food. Calves remain with their mothers during rut in their first fall, but the maternal bond loosens during the following winter, when larger herds form. The young are completely independent by the following spring. Cows are reproductively mature in their third autumn. Males, though physically mature at 2 years of age, are usually inhibited from breeding by older males until they are able to successfully complete for females at the age of 4 years or older.
Predators on elk include bears, wolves, pumas, and man. In areas where large predators are scarce, elk often become overpopulated. The reintroduction of wolves to Yellowstone National Park seems to be controlling the previously overpopulated elk population there.