As many outdoorsmen know, whitetail deer shed their antlers in the late winter. This leads to many folks putting miles on their hiking shoes come spring time, searching for just one of these dropped treasures. Most people may know deer shed their antlers, but many may not know why. Lets get into it.
First things first: What is an antler?
An antler is a branched bone, not a horn as they are sometimes referred to as. They are an extension directly from the skull of the animal. Male animals in the deer family (Cervidae) all tend to grow antlers. This includes whitetail deer, mule deer, elk, moose, and caribou just to name a few here in North America. However, don't be fooled. Female caribou also grow antlers in the far north despite the smaller antler size.
Antlers vs. Horns: Brief Synapsis
As stated above, antlers are a branched bone. This means they are an extension of the skull of the animal. It also means that they are a single structure (no outer shell when in full growth). Other than the female caribou, the majority of the deer family only grow antlers on male species.
Horns are not the same as antlers. Horns are typically grown in the bovine family, as opposed to the Cervidae family. Species in North America may include bison, bighorn sheep, pronghorn and mountain goats. Domestic animals such as cattle, goats, and sheep grow horns, as well. Unlike antlers, horns are a two part structure. The first part of the horn, the internal bone, is connected directly to the skull. Much like an antler, however, it is a permanent bone opposed to an annual bone. The bone is then covered in keratin (yes the same thing as our finger nails!). Horns do not shed and will continue to grow for the duration of the animal's life.
Why do deer shed their antlers?
From when the antlers are just beginning to grow, through the peak of the rut, to the end of the rut - everything based around antler growth can be traced back to testosterone. As most folks may know, testosterone levels in whitetail deer peak during the midst of the rut. This is that critical timeframe when bucks aren't prioritizing food, but rather breeding. At this point a buck will have already been in multiple sparring matches and will be bruised and bloodied, not to mention a possible antler injury from the fighting. Once the rut is over, a buck's focus will shift back to finding food opposed to breeding. During this switch the need for a buck to maintain and keep his antlers drops significantly. This translates to their testosterone levels dropping immensely, in turn, triggering the shedding cycle.
While testosterone is definitely a defining factor, it is not the only regulator that determines when bucks may shed their antlers. Whitetails rely heavily on day length, or rather, the sun. The length of day is a leading cause of determining the testosterone levels in a whitetail. It is the change in daylight that will cue the antler shedding process.
It is fair to note too, that there are cases where bucks will shed their antlers incredibly early in the season. This could occur in November, or even December. This typically happens because the deer is injured in some way. When a buck is wounded, whether that be from a nonfatal shot, vehicle accident, or even just unhealthy - testosterone levels will drop. This is because the buck may no longer be prioritizing breeding, but rather survival. When this happens, the shedding process will be started, simply to help the buck survive by not directing necessary nutrients towards maintaining the antlers.
When looking at a buck’s skull you will see two protrusions of bone, one above each eye. These protrusions of bone are called "pedicles". Pedicles serve as the connector between a buck’s antlers and his skull (allowing for the single structure as highlighted above). Unlike the antler, pedicles serve as permanent parts of a buck’s skeleton. While they do not shed like antlers, they will grow in diameter throughout the lifespan of a buck. When you hear an outdoorsman exclaiming, "that buck had massive bases on him!", it was because of the pedicles. At the base of each antler is the antler burr. The burr's function is to serve as a protective shield at the base of each antler, thus protecting the skin edge where it connects with the pedicle.
It is worth talking about the specialized bone cells that put in the work to effectively "shed the antler". These cells are called osteoclasts. Osteoclasts, by their simplest definition, are bone remodelers. This means that they will absorb old bone tissue. They will congregate towards the base of an antler between the pedicle and burr, and wait for testosterone levels to plummet. Once this happens, they will spring into action and begin breaking down bone tissue between the pedicle and burr of the antler - creating what is called the abscission line. As it weakens it will begin failing to support the weight of the antler. At this point the antler will fall off, or "shed". Finally, the pedicle will grow a scab to begin healing and also begin to grow the next antler.