Only the males have antlers, which start growing in the spring and are shed each winter. The largest antlers may be 1.2 m (4 ft) long and weigh 18 kg (40 lb). Antlers are made of bone which can grow at a rate of 2.5 cm (1 inch) per day. While actively growing, the antlers are covered with and protected by a soft layer of highly vascularised skin known as velvet. The velvet is shed in the summer when the antlers have fully developed. Bull elk may have eight or more tines on each antler; however, the number of tines has little to do with the age or maturity of a particular animal. The Siberian and North American elk carry the largest antlers while the Altai wapiti have the smallest. The formation and retention of antlers is testosterone-driven. After the breeding season in late fall, the level of pheromones released during estrus declines in the environment and the testosterone levels of males drop as a consequence. This drop in testosterone leads to the shedding of antlers, usually in the early winter. Buy Fine art striking Elk in nature landscape photography prints, posters, greeting cards and stock images for licensing. Questions Direct: 303-834-2524 Toll Free: 1-888-682-0122