A whitetail buck's body size depends on many factors, including age, nutrition and an area's deer population. Depending on subspecies, a mature buck may weight 100 to more than 300 pounds.
A buck's antlers are his defining feature. Antlers are actually comprised of bone, and they grow rapidly from spring through late summer. It is believed that antlers evolved as a weapon to gain dominance over other bucks. Each winter a buck sheds his antlers and grows a new pair the next spring.

Outside the breeding season whitetails are sociable by sex. Upon reaching the ripe old age of 16 months, a young buck leaves his familial doe group (his mother actually kicks him out) and disperses to a new home range miles away. He hooks up with other bucks and runs in a bachelor's club. Within this new group, he must constantly prove his worth among his peers. Through ongoing competition, a buck may rise in rank to become a herd's dominant sire.

Dominance is important to bucks. A large buck will stare down opponents. Out of fear, lesser bucks won't dare make eye contact. However, if a brave opponent steps forward, the two duelers crash head to head and lock antlers. A fight ensues until one buck backs down or runs off injured.

A dominant buck's demeanor is proud and unafraid, especially when he postures for does and other bucks during the fall breeding period. With head held high and tail extended straight back, he seems to prance around. Dark hair tufts on an old buck's lower hind legs become erect and move rhythmically to dispense the deer's unique glandular scent. This scent distinguishes the buck as the king of the herd.

A mature buck inhabits a relatively small home range (500 to 3,000 acres) for most of the year, but he travels widely during the rut. A free-roaming buck brimming with testosterone is sometimes called a "dominant floater." Big, healthy bucks lose weight and become stressed out from chasing does and challenging other bucks. Deer enter the post-rut with low fat reserves, and some may perish during a long, harsh winter.