Moose are large, iconic herbivores of northern forests, recognized by their impressive size and, for males, their distinctive headgear. These complex biological structures undergo a remarkable annual cycle and serve various purposes in the life of a bull moose.
Antler Growth and Cycle
Moose antlers are bony structures that grow from specialized points on the skull called pedicels. Antler growth begins anew each spring after shedding, making them one of the fastest-growing tissues in the animal kingdom. Antlers can grow rapidly, sometimes more than an inch per day for a large bull, with a full set developing within three to five months.
During this rapid growth phase, antlers are covered in a soft, fuzzy skin known as velvet. This velvet provides essential nutrients for bone formation. As autumn approaches and antlers near full size, hormonal changes cause the blood supply to cease, leading it to dry and become itchy. Bulls then rub their antlers against trees and shrubs to remove the velvet, a process that also stains and hardens the bone.
After the breeding season, typically November to March, bull moose shed their antlers. This annual shedding is triggered by decreasing daylight and a drop in testosterone, weakening the connection between the antler and pedicel. Shedding these heavy structures, which can weigh up to 40 pounds, helps conserve energy during colder winter months.
Primary Functions of Antlers
Antlers primarily function in male competition during the breeding season, known as the rut. Their size and shape indicate a male moose’s health, age, and genetic fitness. Larger antlers signal strength and maturity, attracting females and deterring rival males without direct confrontation.
During the rut, bull moose engage in ritualized dominance displays, often involving parallel walking to show off size and antler spread. They may also thrash antlers against vegetation to demonstrate power and aggression. These displays often prevent physical fights, as a smaller or weaker male may retreat when faced with a more dominant opponent.
If displays are insufficient, rival males with similar antler sizes may engage in physical combat. These clashes involve locking antlers and pushing to secure breeding rights. While serious injuries are possible, and occasionally antlers can become interlocked leading to death, fights are typically brief and intense.
Antlers Versus Horns
Antlers are distinct from horns. They are made entirely of bone and are shed and regrown annually. They typically grow only on males, with the exception of caribou, where both sexes grow antlers.
Horns, in contrast, are permanent structures that are never shed and continue to grow throughout an animal’s life. They consist of a bony core covered by a keratin sheath, the same material found in human hair and fingernails. Horns are found on animals like cattle, sheep, and goats; in many species, both males and females possess them.