Deer are known for their impressive headgear, often referred to as “horns.” These structures are unique to this family of mammals. Understanding their composition, growth, and purpose reveals a fascinating aspect of deer biology.
Antlers and Horns: Understanding the Difference
While often confused, antlers and horns are distinct biological structures. Deer, along with other Cervidae members like moose and elk, possess antlers. Antlers are made entirely of bone, growing as skull extensions. They are typically branched, shed, and regrown annually, a process unique among mammals with headgear.
In contrast, true horns are found on bovids like cattle, sheep, goats, and bison. Horns consist of a bony core covered by a permanent outer sheath made of keratin, the same protein found in human fingernails. Unlike antlers, horns are generally unbranched and are never shed, growing continuously throughout an animal’s life. Both males and females of horned species often bear these permanent structures.
What Antlers Are Made Of
Deer antlers are composed primarily of bone, distinguishing them from the keratin-covered horns of other animals. During their rapid growth phase, antlers are covered by a highly vascularized skin known as “velvet.” This velvet contains blood vessels, nerves, and fibrous tissue, supplying oxygen and nutrients to the rapidly growing bone underneath.
The velvet nourishes the developing antler, which is among the fastest-growing tissues in the animal kingdom. As the antler matures and calcifies, the blood supply to the velvet diminishes. The velvet then dries, shrivels, and is shed, revealing the hard, dense bone of the mature antler. Mature antlers are similar in composition to compact skeletal bone.
The Annual Antler Cycle
The growth and shedding of antlers follow an annual cycle, influenced by seasonal changes in daylight and hormones. Antler growth begins from bony structures on the skull called pedicles, which are permanent in male deer. This process starts in late spring, with antlers growing rapidly.
During this growth phase, antlers are covered in velvet, which supports their development. As summer progresses, rising testosterone levels trigger the calcification and hardening of the antlers, causing the velvet to dry out and peel away. Deer often rub their antlers against trees and brush to remove the remaining velvet, a process that also polishes and strengthens the exposed bone.
After the breeding season, in late winter or early spring, a drop in testosterone levels causes a layer of tissue to form at the base of the antler, weakening its connection to the pedicle. This leads to the annual shedding of the antlers, a process that does not cause the deer pain. New antler growth begins almost immediately from the pedicles, restarting the cycle.
Why Deer Have Antlers
Antlers serve several biological functions for male deer, primarily related to reproduction and social hierarchy. They are used in male-to-male competition for dominance and access to females during the breeding season, known as the rut. Deer use their antlers to spar, display strength, and establish social status within their herds.
The size and condition of a male’s antlers can also signal his health, age, and genetic fitness to potential mates. Larger, more developed antlers may indicate a male’s ability to acquire sufficient nutrition, making him a more attractive mate. While primarily for competition and display, antlers can also provide a form of defense against predators, though this is not their main evolutionary purpose.