In late winter or early spring, white-tailed buck deer (Odocoileus virginianus), develop two hard, bony antlers that are elongated and branched. They are on the forehead, between the ears and are used for defense and in battle with other bucks to secure mates. Bucks with the largest antlers posture and sometimes avoid battle by intimidating other bucks.
Antler growth is amazing. They begin slowly, but then growth speeds up to an amazing level. They are initially covered by "velvet" that contains blood vessels that provide the nutrients necessary for growth. The antlers of a mature buck are very impressive, when fully developed and as the breeding season or "rut" approaches, the deer begin to rub the antlers on shrubs and trees to remove the velvet and polish the antlers.
One of the most amazing things about deer is the fact that in the fall they shed the antlers that were displayed so proudly the previous year. The antlers are shed after the breeding season (called the rut) is past. Usually the breeding season is in October or November in most states. After the mating season and hunting season are over, the bucks are in a very stressful period. They do not eat properly during the rut and they lose weight. Many are injured in battles for available does and some die. The one that survive have significant drops in testosterone levels. This change in hormones causes the antlers to drop.
The change in light levels is the triggering mechanism that causes the testosterone levels to drop and in turn this causes the antler loss. This change in hormone level causes an abscission layer where the tissue breaks down. This causes the base of the antler and the pedicle to separate. The pedicle is the site on the skull where the antler initially developed.
Distance from the equator seems to have an effect on antler loss. In northern climates, the period of antler loss is shorter and more defined. In southern climates, the period is spread out over a much longer period.
Dropped antlers are called "sheds" or "drops". Hunters look for sheds to save as trophies. In addition, this provides valuable information for the next hunting season by identifying which bucks survived the previous season. Shed antlers are used to make lamps, knife handles, candle holders and all manner of decorative items for the home or hunting lodge.
Why deer evolved into creatures that shed antlers rather than retaining horns similar to cattle, sheep or goats is a mystery. There are many hypotheses, but the actual reason is only conjecture. Regardless, it is one of the miraculous occurrences in the animal kingdom and is interesting to observe.