Moose are known for their impressive headgear. These bony structures, called antlers, are not horns. Unlike horns, which are permanent and made of keratin over a bony core, moose antlers are true bone extensions that grow from the skull and are shed annually.
The Annual Antler Shedding Cycle
Male moose, often called bulls, typically shed their antlers after the breeding season, known as the rut. This usually occurs between December and January, though exact timing can vary. In some northern regions, shedding might begin as early as December.
A decline in testosterone levels following the breeding season triggers antler shedding. This hormonal shift weakens the connection between the antler and the pedicle, which is the bony base on the moose’s skull from which the antler grows. Special bone cells called osteoclasts resorb calcium at this junction, further loosening the antler’s attachment.
Shedding antlers is painless for the moose. Mature antlers lack nerves and blood vessels, so detachment causes no discomfort, similar to losing a baby tooth. While antlers may fall off naturally, moose sometimes rub them against trees or bushes to help dislodge them, especially if one has already fallen and created an imbalance.
Factors Influencing Shedding Timing
Several factors influence shedding timing. The age of the bull moose plays a role, with older individuals often shedding their antlers earlier in the season. After about 10 to 12 years, a bull’s antlers may even begin to grow back misshapen in subsequent years.
Health and nutritional status also impact antler retention. Well-fed moose may retain them longer, while those in poorer health might shed earlier. Environmental factors, like geographical location and winter severity, also affect shedding times. Moose in colder climates might shed sooner to conserve energy. The amount of daylight, or photoperiod, directly influences the hormonal changes that regulate the antler cycle.
The Antler Regrowth Process
After shedding, moose begin growing almost immediately, typically starting in the spring. This regrowth is incredibly rapid, making antler tissue one of the fastest-growing tissues in the animal kingdom, with some antlers growing over an inch per day. The developing antlers are covered in a soft, fuzzy skin known as velvet.
Velvet is rich in blood vessels and nerves, which supply the essential nutrients and oxygen needed for the rapid bone growth. As summer progresses and the antlers reach their full size, typically by late summer or early fall, the velvet begins to dry and lose its blood supply. Moose then rub their antlers against trees and shrubs to scrape off this dried velvet, revealing the hardened, polished bone beneath.
Once the velvet is shed, the fully grown and hardened antlers are ready for their primary purpose: display and sparring during the autumn rut. These impressive structures, which can span up to six feet wide and weigh up to 40 pounds each, serve as a visual display of dominance to attract mates and engage in ritualized combat with rival bulls. The annual regrowth ensures that bulls have a fresh, strong set of antlers each year for these important reproductive behaviors.