Bull Elk, ColoradoGrown and shed annually, a bull elk’s antlers can be more than four feet wide and weigh up to 40 pounds, making them one of the fastest-growing bones in the world. Bulls use their “racks” during the fall rut to spar with rivals and impress females, locking antlers in dramatic battles that determine mating rights. Covered in soft, fuzzy velvet during the growth phase, antlers are rich with blood vessels and nerves until they harden and the velvet is shed. Each rack is an indication of age, health, and dominance in the life of an elk. This big boy was photographed in Colorado’s Rocky Mountain National Park back in 2009. Nikon D300 with Nikkor 200-400mm lens (at 400mm) ISO 400, f/6.3 at 1/250th of a second.